Illumination optical system, exposure apparatus, and exposure method with polarized switching device

ABSTRACT

An illumination optical system for, when installed in an exposure system, realizing a suitable illumination condition by varying the polarized state of the illumination light according to the pattern characteristics of the mask while suppressing the loss of the intensity of the light. The illumination optical system has a light source unit for supplying a linearly polarized light for illuminating surfaces to be illuminated therewith, and a polarized state changing device for changing the polarized state of the illuminating light from a predetermined polarized state to a nonpolarized state and vice versa. The polarized state changing device is arranged in the optical path between the light source unit and the surfaces to be illuminated. The polarized state changing device can be removed from the illumination optical path and has a depolarizer for selectively depolarizing the incident linearly polarized light.

RELATED APPLICATIONS

This is a Continuation-In-Part of International Application No.PCT/JP03/015447 filed Dec. 2, 2003. The entire disclosure of saidInternational Application No. PCT/JP03/015447 is incorporated byreference herein in its entirety. The disclosure of each of thefollowing priority applications is herein incorporated by reference inits entirety: Japanese Patent Application No. 2002-351186 filed Dec. 3,2002; Japanese Patent Application No. 2003-201079 filed Jul. 24, 2003;and Japanese Patent Application No. 2003-338447 filed Sep. 29, 2003.

BACKGROUND

This invention relates to illumination optical systems, exposureapparatus and exposure methods. In particular, this invention relates toexposure apparatus for manufacturing micro devices, such assemiconductor elements, imaging elements, flat panel displays such asliquid crystal display elements and thin-film magnetic heads, usinglithographic processes.

In typical exposure apparatus of this type, a secondary light source,which functions as a substantially planar light source composed of aplurality of light sources, is formed by a light beam from a lightsource that is transmitted through a fly's-eye lens that functions as anoptical integrator. The light beams from the secondary light source areincident to a condenser lens after being regulated through an aperturediaphragm positioned near a rear focal plane of the fly's-eye lens.

The light beams converged by the condenser lens illuminatesuperimposingly a mask on which a predetermined pattern is formed. Thelight transmitted through mask pattern forms an image on a wafer througha projection optical system. As a result, the mask pattern is projectedand exposed (transferred) onto the wafer. Because the pattern formed onthe mask is highly integrated, it is necessary to obtain a uniformillumination distribution on the wafer in order to accurately transferthe micro patterns onto the wafer.

Accordingly, attention has been given to a technology in which acircular secondary light source is formed on the rear focal plane of thefly's-eye lens, and illumination coherency σ (σ=an aperture diaphragmdiameter/a pupil diameter of a projection optical system; or σ=anexit-side numerical aperture of an illumination optical system/anincident-side numerical aperture of the projection optical system) ischanged by varying a size of the secondary light source. Moreover,attention has been given to a technology in which a depth of focus andresolution of the projection optical system are improved by forming anannular or quadrupole secondary light source.

In the above-described conventional exposure apparatus, normal circularillumination is performed with a circular secondary light source, andmodified illumination (annular or quadrupole illumination) is performedwith an annular or quadrupole secondary light source, depending on thecharacteristics of the mask pattern. However, it is generally the casethat, regardless of the characteristics of the mask pattern, the mask isilluminated with light whose polarized state is not changed, that is,light in a nonpolarized state. Appropriate illumination conditions thatare required to precisely transfer the mask pattern onto the wafer arenot always secured.

SUMMARY OF THE INVENTION

A first object of this invention is to provide an illumination opticalsystem that, when installed on an exposure apparatus, allows theachievement of appropriate illumination conditions by changing thepolarized state of the illumination light in accordance with thecharacteristics of the mask pattern, while controlling a loss of a lightamount.

Another object of this invention is to provide an exposure apparatus andan exposure method that uses an illumination optical system that changesthe polarized state of the illumination light in accordance with thecharacteristics of the mask pattern, to perform excellent exposure underappropriate illumination conditions that are accomplished in accordancewith the characteristics of the mask pattern.

According to a first aspect, an illumination optical system, arranged inan optical path between a linearly polarized light source and anilluminated surface, includes a polarized state switching device that ispositioned in a light path between the light source and the illuminatedsurface. The polarized state switching device switches the polarizedstate of the light that illuminates the illuminated surface between apredetermined polarized state and a nonpolarized state. It is preferablethat the polarized state switching device is insertable into andremovable from an illumination light path and includes a depolarizerthat selectively unpolarizes the incident linearly polarized light.

According to a second aspect, an illumination optical system thatilluminates an illuminated surface under a predetermined polarized statewith light from a light source includes a light directing device thatdirects the light from the light source to the illuminated surface andis positioned in a light path between the light source and theilluminated surface, and a polarized state fluctuation correcting devicethat corrects fluctuations in the polarized state on the illuminatedsurface and that is positioned in the light path between the lightsource and the illuminated surface.

According to a third aspect, an illumination optical system thatilluminates an illuminated surface under a predetermined polarized statewith light from a light source includes a light directing device thatdirects the light from the light source to the illuminated surface andis positioned in a light path between the light source and theilluminated surface, and a polarized state stabilizing device thatstabilizes the polarized state on the illuminated surface and that ispositioned in the light path between the light source and theilluminated surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the followingdrawings of exemplary embodiments in which like reference numeralsdesignate like elements, and in which:

FIG. 1 is a diagram schematically showing a structure of an exposureapparatus equipped with an illumination optical system according to anexemplary embodiment of this invention;

FIG. 2A is a diagram showing an annular secondary light source formedfor annular illumination;

FIG. 2B is a quadrupole secondary light source formed for quadrupoleillumination;

FIGS. 3A and 3B are diagrams showing a dipole secondary light sourceformed for dipole illumination;

FIG. 4 is a diagram schematically showing a structure of the first phasemember and a depolarizer;

FIG. 5 is a diagram schematically showing a structure of a polarizedstate switching device according to a first exemplary modification;

FIG. 6 is a diagram schematically showing a structure of a polarizedstate switching device according to a second exemplary modification;

FIG. 7 is a diagram schematically showing a structure of a polarizedstate switching device according to a third exemplary modification;

FIG. 8 is a diagram schematically showing a structure of a depolarizeraccording to an exemplary modification;

FIG. 9 is a diagram schematically showing an internal structure of abeam matching unit positioned between the light source and the polarizedstate switching device shown in FIG. 1;

FIG. 10 is a diagram explaining a fluorite crystal orientation;

FIG. 11 is a diagram schematically showing an example in which aquarter-wave plate, which converts elliptically polarized light tolinearly polarized light, is additionally provided for the polarizedstate switching device;

FIG. 12 is a flow chart of a method used for obtaining a liquid crystaldisplay element as a micro device;

FIG. 13 is a flow chart of a method for obtaining a semiconductorelement as a micro device;

FIG. 14 is a diagram schematically explaining an example in which a maskis illuminated with light in the linearly polarized state under dipoleillumination;

FIG. 15 is a diagram schematically explaining an example in which a maskis illuminated with light in the linearly polarized state under circularillumination;

FIG. 16 is a diagram schematically showing a structure in which theexposure apparatus shown in FIG. 1 is additionally provided with apolarization monitor for detecting the polarized state of theillumination light;

FIG. 17 is a perspective view schematically showing an internalstructure of the polarization monitor shown in FIG. 16;

FIG. 18 is a flow chart of a method for adjusting a crystal optic axisfor the quarter-wave plate and a crystal optic axis for a half-waveplate in the polarized state switching device shown in FIG. 11;

FIG. 19 is a diagram showing changes in output of the polarizationmonitor at each angular position of the crystal optic axis for thehalf-wave plate when the crystal optic axis for the quarter-wave plateis fixed at a normal angular position of −45 degrees;

FIG. 20 is a diagram showing changes in output of the polarizationmonitor at each angular position of the crystal optic axis for thehalf-wave plate when the crystal optic axis for the quarter-wave plateis set at various angular positions;

FIG. 21 is a diagram showing changes in output contrast of thepolarization monitor at various angular positions for the crystal opticaxis for the quarter-wave plate;

FIG. 22 is a diagram showing changes in output of the polarizationmonitor at each angular position of the crystal optic axis for thehalf-wave plate when the crystal optic axis of the quarter-wave plate isfixed at the first angular position for converting the ellipticallypolarized light to a linearly-polarized light;

FIG. 23 is a diagram schematically showing a structure of an exposureapparatus having an illumination pupil distribution forming device,which has a different structure from the exposure apparatus shown inFIG. 1 or FIG. 16;

FIG. 24 is a diagram schematically showing a structure of a conicalaxicon system positioned in a light path between a front-side lens groupand a rear-side lens group of an afocal lens shown in FIG. 23;

FIG. 25 is a diagram explaining functions of the conical axicon systemwith respect to the secondary light source formed with an annularillumination in the exemplary modification shown in FIG. 23;

FIG. 26 is a diagram explaining functions of a zoom lens with respect tothe second light source formed with the annular illumination in theexemplary modification shown in FIG. 23;

FIG. 27 is a diagram schematically showing a structure of the firstcylindrical lens pair and the second cylindrical lens pair, which arepositioned in the light path between the front-side lens group and therear-side lens group of the afocal lens shown in FIG. 23;

FIG. 28 is a diagram explaining the functions of the first cylindricallens pair and the second cylindrical lens pair with respect to thesecondary light source formed with the annular illumination of theexemplary modification shown in FIG. 23;

FIG. 29 is a diagram explaining the functions of the first cylindricallens pair and the second cylindrical lens pair with respect to thesecondary light source formed with the annular illumination in theexemplary modification shown in FIG. 23; and

FIG. 30 is a diagram explaining the functions of the first cylindricallens pair and the second cylindrical lens pair with respect to thesecondary light source formed with the annular illumination in theexemplary modification shown in FIG. 23.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

According to a first embodiment, an illumination optical system that hasa light source for providing linearly polarized light and thatilluminates an illuminated surface with the light from the light sourceincludes a polarized state switching device that is positioned in alight path between the light source and the illuminated surface and thatswitches the polarized state of the light that illuminates theilluminated surface between a predetermined polarized state and anonpolarized state.

The polarized state switching device is insertable into and removablefrom an illumination light path and includes a depolarizer thatselectively unpolarizes the incident linearly polarized light.

According to the first embodiment, the polarized state switching devicevaries a polarization plane of the linearly polarized light if thepredetermined polarized state is a linearly polarized state. Inaddition, it is preferable that the polarized state switching deviceincludes a phase member for selectively changing a polarization plane ofthe incident linearly polarized light. In this case, the phase memberhas a half-wave plate with a crystal optic axis that is rotatable aboutan optical axis of the illumination optical system.

In addition, according to the first embodiment, the depolarizer includesa crystal prism having a crystal optic axis that is rotatable about anoptical axis of the illumination optical system. In addition, it ispreferable that the depolarizer includes a polarized beam splitter and areflection system that returns the light reflected by the polarized beamsplitter back to the polarized beam splitter by reflecting the lightplural times in a plane, such that a light path of light that istransmitted through the polarized beam splitter and a light path oflight reflected by the polarized beam splitter substantially match eachother. It is preferable that the polarized beam splitter and thereflection system are integrally rotatable about the optical axis of theillumination optical system.

In addition, according to the first embodiment, the depolarizer includesa polarized beam splitter and a reflection system that returns the lightreflected by the polarized beam splitter back to the polarized beamsplitter by reflecting the light plural times in a plane such that alight path of light that is transmitted through the polarized beamsplitter and a light path of light reflected by the polarized beamsplitter substantially match each other. It is preferable that thepolarized beam splitter and the reflection system are integrallyinsertable into and removable from an illumination light path.

In addition, according to the first embodiment, the polarized stateswitching device further includes a second phase member for convertingincident elliptically polarized light into linearly polarized light. Inthis case, it is preferable that the second phase member includes aquarter-wave plate having a crystal optic axis that is rotatable aboutan optical axis of the illumination optical system.

Further, according to the first embodiment, a light transmissive memberis positioned in the light path between the light source and thepolarized state switching device and is formed by a cubic system(isometric system) crystal material, and the light transmissive memberis oriented such that a traveling direction of the light becomes closerto a crystal orientation <111> or <100> than to a crystal orientation<110>. In this case, it is preferable that the light transmissive memberis positioned in the light path between the polarized state switchingdevice and the illuminated surface, and is formed by a cubic systemcrystal material, and the light transmissive member is oriented suchthat a traveling direction of the light becomes closer to a crystalorientation <111> or <100> than to a crystal orientation <110>.

It is preferable that the light transmissive member includes an opticalmember fixedly positioned in the light path, and that an optical axis ofthe optical member substantially matches the crystal orientation <111>or <100>. In addition, it is preferable that the light transmissivemember includes a rectangular prism as a rear surface reflection mirror,that an incident surface and an exit surface of the rectangular prismsubstantially match a crystal plane {100}, and that a reflection surfaceof the rectangular prism substantially matches a crystal plane {110}. Inaddition, it is preferable that the light transmissive member includes aplane parallel plate for moving light entering along the optical axis inparallel, and the light transmissive member is provided in the lightpath and is inclinable with respect to the optical axis. It ispreferable that the optical axis of the plane parallel platesubstantially matches the crystal orientation <100>.

In addition, according to the first embodiment, the illumination opticalsystem also includes an illumination pupil distribution forming devicethat forms a predetermined light intensity distribution on or adjacentto a pupil plane of the illumination optical system, a changing devicethat changes at least one of a shape and a size of the predeterminedlight intensity distribution, and a light direction optical system thatdirects a light beam from the predetermined light intensity distributionto the illuminated surface. In this case, it is preferable that thepolarized state switching device changes a polarized state of the lightthat illuminates the illuminated surface in accordance with the changein at least one of the shape and the size of the predetermined lightintensity distribution. In addition, it is preferable that the polarizedstate switching device switches the polarized state of the light thatilluminates the illuminated surface between a linearly polarized stateand a nonpolarized state in accordance with the change in at least oneof the shape and the size of the predetermined light intensitydistribution.

In addition, according to the first embodiment, in the predeterminedpolarized state, an S1 component of a Stokes parameter of the lightsatisfies a condition 0.6≦|S1|. In addition, it is preferable that inthe nonpolarized state, S1 and S2 components of a Stokes parameter ofthe light satisfy conditions |S1|<0.1 and |S2|≦0.1. Moreover, it ispreferable that the illumination optical system further includes apolarized state fluctuation correcting device that corrects fluctuationsof the polarized state on the illuminated surface, and that thepolarized state fluctuation correcting device is positioned in the lightpath between the light source and the illuminated surface. In this case,the polarized state fluctuation correcting device includes apolarization monitor positioned in the light path between the polarizedstate switching device and the illuminated surface to detect thepolarized state of the light, and a controller that controls thepolarized state switching device in response to an output from thepolarization monitor.

In addition, according to the first embodiment, the polarized stateswitching device includes a half-wave plate having a crystal optic axisthat is rotatable about the optical axis of the illumination opticalsystem, and a quarter-wave plate having a crystal optic axis that isrotatable about the optical axis of the illumination optical system. Inresponse to changes in detection results obtained from the polarizationmonitor when respectively changing the crystal optic axes of thequarter-wave plate and the half-wave plate, the controller adjusts anangular position of the crystal optic axis of the quarter-wave plate toa predetermined position for converting incident elliptically polarizedlight into linearly polarized light, and an angular position of thecrystal optic axis of the half-wave plate to a predetermined positionfor converting incident linearly polarized light to linearly polarizedlight that has a polarization plane in a predetermined direction. Inthis case, it is preferable that the controller adjusts the angularposition of the crystal optic axis of the quarter-wave plate to a firstangular position, at which a contrast for changes in the S1 component ofthe Stokes parameter in the detection result becomes substantiallymaximum, and changes the angular position of the crystal optic axis ofthe half-wave plate to a second angular position at which the S1component of the Stokes parameter in the detection result becomessubstantially maximum or substantially minimum while the crystal opticaxis of the quarter-wave plate is set at the first angular position.

In addition, according to the first embodiment, the polarization monitoris positioned in the light path between the polarized state switchingdevice and the illuminated surface and includes a beam splitter thatextracts from the light path reflected light or transmitted light havinga polarized state that is different from the polarized state of theincident light and a light intensity detector that detects the intensityof the reflected light or the transmitted light extracted by the beamsplitter. The polarized state of the incident light to the beam splitteris detected based on an output of the light intensity detector. In thiscase, it is preferable that the beam splitter has reflectivity ortransmissivity, in which intensity Ip for p-polarized light andintensity Is for s-polarized light included in the reflected light orthe transmitted light satisfy a condition that an intensity ratio Ip/Isis less than ½ (Ip/Is<½) or more than 2 (Ip/Is>2).

In addition, according to the first embodiment, the illumination opticalsystem further includes an illumination pupil distribution formingdevice that forms a predetermined light intensity distribution on oradjacent to a pupil plane of the illumination optical system. Theillumination pupil distribution forming device forms two areas having ahigh light intensity distribution that are spaced along a direction ofthe pupil plane or a surface adjacent thereto that corresponds to apredetermined first direction on the illuminated surface. The polarizedstate switching device sets the polarized state of the light thatilluminates the illuminated surface from the two areas having a highlight intensity distribution to a linearly polarized state that has apolarization plane in a direction substantially orthogonal to thepredetermined first direction. In this case, the two areas having a highlight intensity distribution are formed symmetrically about the opticalaxis of the illumination optical system, and a value σo defined by aratio φo/φp satisfies a condition 0.7≦σo where φo is a diameter of acircle about the optical axis that circumscribes the two areas having ahigh light intensity distribution, and φp is a diameter of the pupilplane. It is preferable that the two areas having a high light intensitydistribution are formed symmetrically about the optical axis of theillumination optical system, and a value σo defined by a ratio φo/φp andσi defined by a ratio φi/φp satisfy a condition 0.5≦σi/σo where φo is adiameter of a circle about the optical axis that circumscribes the twoareas having a high light intensity distribution, φp is a diameter ofthe pupil plane, and φi is a diameter of a circle about the optical axisthat inscribes the two areas having a high light intensity distribution.

In a second embodiment, an illumination optical system that illuminatesan illuminated surface under a predetermined polarized state with lightfrom a light source includes a light directing device that directs thelight from the light source to the illuminated surface and is positionedin a light path between the light source and the illuminated surface,and a polarized state fluctuation correcting device that correctsfluctuations in the polarized state on the illuminated surface and ispositioned in the light path between the light source and theilluminated surface.

According to the second embodiment, the polarized state fluctuationcorrecting device includes a polarized state adjusting device thatadjusts the polarized state on the illuminated surface and is positionedin the light path between the light source and the illuminated surface,a polarization monitor that detects the polarized state of the light andis positioned in the light path between the light source and theilluminated surface, and a controller that controls the polarized stateadjusting device in accordance with an output from the polarizationmonitor. In this case, it is preferable that the polarized stateadjusting device includes an adjustable phase plate positioned in thelight path between the light source and the polarization monitor. Inaddition, according to the second embodiment, it is preferable that thelight directing device includes an optical member having characteristicsthat change the polarized state of incident light and then ejects thatlight. The optical member may be formed by a crystal optical material.

In a third embodiment, an illumination optical system that illuminatesan illuminated surface with light from a light source includes a lightdirecting device that directs the light from the light source to theilluminated surface and is positioned in a light path between the lightsource and the illuminated surface, and a polarized state stabilizingdevice that stabilizes the polarized state on the illuminated surfaceand is positioned in the light path between the light source and theilluminated surface.

According to the third embodiment, the polarized state stabilizingdevice includes a polarized state adjusting device that adjusts thepolarized state on the illuminated surface and is positioned in thelight path between the light source and the illuminated surface, apolarization monitor that detects the polarized state of the light andis positioned in the light path between the light source and theilluminated surface, and a controller that controls the polarized stateadjusting device in accordance with an output from the polarizationmonitor. In this case, it is preferable that the light directing deviceincludes an optical member having characteristics that change thepolarized state of incident light and then ejects that light. Theoptical member may be formed by a crystal optical material.

In addition, according to the third embodiment, the polarized statestabilizing device includes a light transmissive member formed by acubic system crystal material that is positioned in the light pathbetween the light source and the illuminated surface. In this case, itis preferable that the light transmissive member is oriented such that atraveling direction of the light becomes closer to a crystal orientation<111> or <100> than a crystal orientation <110>. In addition, it ispreferable that the light transmissive member includes an optical memberfixedly positioned in the light path and that an optical axis of theoptical member is oriented to substantially match the crystalorientation <111> or <100>. It may instead be preferable that the lighttransmissive member includes a rectangular prism as a rear surfacereflection mirror, that an incident surface and an exit surface of therectangular prism are oriented to substantially match a crystal plane{100}, and that a reflection surface of the rectangular prism isoriented to substantially match a crystal plane {110}. It may instead bepreferable that the light transmissive member includes a plane parallelplate for moving light entering along the optical axis in parallel andthat is provided in the light path and is inclinable with respect to theoptical axis, and that the optical axis of the plane parallel plate isoriented to substantially match the crystal orientation <100>.

According to a fourth embodiment, a method for adjusting an illuminationoptical system that illuminates an illuminated surface in apredetermined polarized state by light from a light source includes awavelength plate setting step that sets a quarter-wave plate in anillumination light path of the illumination optical system such that acrystal optic axis of the quarter-wave plate is set at a predeterminedangular position, and sets a half-wave plate in the illumination lightpath such that a crystal optic axis of the half-wave plate is set at apredetermined angular positioned. Based on a result of detection of thepolarized state of the light in the light path between a polarized stateswitching device and the illuminated surface, the crystal optic axes ofthe quarter-wave plate and the half-wave plate are respectively changed.The wavelength plate setting step sets the crystal optic axis of thequarter-wave plate at a desired position for converting incidentelliptically polarized light into linearly polarized light and thecrystal optic axis of the half-wave plate at a standard position forconverting incident linearly polarized light into linearly polarizedlight that has a polarization plane in a predetermined direction.

According to the fourth embodiment, the crystal optic axis of thequarter-wave plate is set at a first angular position, at which acontrast for changes in an S1 component of a Stokes parameter becomessubstantially maximum in the detection result, and the crystal opticaxis of the half-wave plate is set at a second angular position at whichthe S1 component of the Stokes parameter becomes substantially maximumor substantially minimum in the detection result while the crystal opticaxis of the quarter-wave plate is set at the first angular position. Inaddition, it is preferable that the method also includes an illuminationpupil forming step that forms a predetermined light intensitydistribution on or adjacent to a pupil plane of the illumination opticalsystem by the light from the light source, an illumination pupilchanging step that changes at least one of a shape and a size of thepredetermined light intensity distribution, and a wavelength plateresetting step that resets at least one of the crystal optic axes of thequarter-wave plate and the half-wave plate.

According to a fifth embodiment, an exposure apparatus that includes theillumination optical system described in the first-third embodiments orthe illumination optical system adjusted by the adjustment methoddescribed in the fourth embodiment is provided.

According to the fifth embodiment, the exposure apparatus also includesa projection optical system that is positioned in the light path betweena first plane at which the mask is positioned, and a second plane atwhich the photosensitive substrate is positioned, and that forms animage of a pattern of the mask onto the second plane, a pupil intensitydistribution forming device that forms a predetermined light intensitydistribution at a position conjugate to the pupil of the projectionoptical system or a position adjacent thereto, and a pupil intensitydistribution changing device that changes at least one of a shape and asize of the predetermined light intensity distribution. In this case, itis preferable that the exposure apparatus also includes a polarizedstate changing device that is positioned in the light path between thelight source and the illuminated surface and changes the polarized stateof the light that illuminates the illuminated surface. The pupilintensity distribution changing device preferably changes at least oneof the shape and the size of the predetermined light intensitydistribution in accordance with pattern characteristics of the mask. Thepolarized state changing device preferably changes the polarized stateof the light that illuminates the illuminated surface in accordance withat least one of the shape and the size of the predetermined lightintensity distribution. In addition, it is preferable that the polarizedstate changing device includes a polarized state switching device thatswitches the polarized state of the light that illuminates theilluminated surface between a predetermined polarized state and anonpolarized state, and that the polarized state switching deviceswitches between the predetermined polarized state and the nonpolarizedstate in accordance with a change in at least one of the shape and thesize of the predetermined light intensity distribution.

Furthermore, according to the fifth embodiment, the pupil intensitydistribution forming device forms two areas having a high lightintensity distribution that are spaced away from each other along apitch direction of a line-and-space pattern formed on the mask. Thepolarized state changing device sets the polarized state of the lightthat illuminates the illuminated surface from the two areas having ahigh light intensity distribution to a linearly polarized state that hasa polarization plane in a direction orthogonal to the pitch direction.Instead, it may be preferable that the pupil intensity distributionforming device forms one area having a high light intensity distributionsubstantially about the optical axis of the illumination optical system,and that the polarized state changing device sets the polarized state ofthe light that illuminates the illuminated surface from the one areahaving a high light intensity distribution to the linearly polarizedstate that has a polarization plane in a direction substantiallyorthogonal to the pitch direction of the line-and-space pattern formedon a phase shift mask as the mask. In this case, it is preferable thatthe value σ that is defined by a ratio φ/φp satisfies a condition σ≦0.4where φis a size of the one area having a high light intensitydistribution, and φp is a diameter of the pupil plane.

In a sixth embodiment, an exposure method includes an illumination stepthat illuminates a mask through the illumination optical system of thefirst-third embodiments or an illumination optical system adjusted inaccordance with the adjustment method of the fourth embodiment, and anexposure step that exposes a pattern on the mask onto the photosensitivesubstrate positioned on the illuminated surface.

According to the sixth embodiment, the exposure method further includesa projection step that forms an image of the pattern on the mask using aprojection optical system, a pupil intensity distribution forming stepthat forms a predetermined light intensity distribution at a positionconjugate to the pupil of the projection optical system or a positionadjacent thereto, and a pupil intensity distribution changing step thatchanges at least one of a shape or a size of the predetermined lightintensity distribution. In this case, it is preferable that the pupilintensity distribution changing step changes at least one of the shapeand the size of the predetermined light intensity distribution inaccordance with pattern characteristics of the mask, and that theexposure method also includes a polarized state changing step thatchanges a polarized state of the light that illuminates the illuminatedsurface in accordance with a change in the at least one of the shape andthe size of the predetermined light intensity distribution.

In addition, according to the sixth embodiment, the pupil intensitydistribution forming step forms two areas having a high light intensitydistribution spaced away from each other along a pitch direction of aline-and-space pattern formed on the mask, and the exposure method alsoincludes a step that sets the polarized state of the light thatilluminates the illuminated surface from the two areas having a highlight intensity distribution to a linearly polarized state that has apolarization plane in a direction substantially orthogonal to the pitchdirection. In this case, it is preferable that the two areas having ahigh light intensity distribution are formed symmetrically about theoptical axis of the illumination optical system, and that a value σodefined by a ratio φo/φp satisfies a condition 0.7≦σo where φo is adiameter of a circle about the optical axis that circumscribes the twoareas having a high light intensity distribution, and φp is a diameterof the pupil plane. In addition, it is preferable that the two areashaving a high light intensity distribution are formed symmetricallyabout the optical axis of the illumination optical system, and that avalue σo defined by a ratio φo/φp and σi defined by a ratio φi/φpsatisfy a condition 0.5≦σi/σo where φo is a diameter of a circle aboutthe optical axis that circumscribes the two areas having a high lightintensity distribution, φp is a diameter of the pupil plane, and φi is adiameter of a circle about the optical axis that inscribes the two areashaving a high light intensity distribution.

In a seventh embodiment, an exposure method for exposing a pattern on amask positioned at a first plane onto a photosensitive substratepositioned at a second plane includes a first step that provideslinearly polarized light, a second step that illuminates the mask withthe light provided in the first step, a third step that exposes thepattern on the mask illuminated in the second step onto thephotosensitive substrate, and a fourth step that switches a polarizedstate of the light on the second plane between a predetermined polarizedstate and a nonpolarized state while controlling a loss of a lightamount.

According to the seventh embodiment, the fourth step includes a stepthat varies a polarization plane for linearly polarized light. Inaddition, it is preferable that the third step includes a step thatforms an image of the pattern on the mask onto the second plane using aprojection optical system, and that the exposure method also includes afifth step that forms a predetermined light intensity distribution at aposition conjugate to a pupil of the projection optical system or aposition adjacent thereto, a sixth step that changes at least one of ashape or a size of the predetermined light intensity distribution, and aseventh step that changes a polarized state of the light thatilluminates the illuminated surface in accordance with the change in atleast one of the shape and the size of the predetermined light intensitydistribution.

In an eighth embodiment, an exposure method for exposing a pattern on amask positioned at a first plane onto a photosensitive substratepositioned at a second plane includes a first step that provides light,a second step that illuminates the mask with light provided in the firststep, a third step that exposes the pattern on the mask illuminated inthe second step onto the photosensitive substrate, and a fourth stepthat corrects fluctuations of a polarized state of the light on thesecond plane.

According to the eighth embodiment, the exposure method also includes afifth step that detects the polarized state of the light, and the fourthstep includes a step that adjust the polarized state on the second planebased on the polarized state of the light detected in the fifth step.

In a ninth embodiment, an illumination optical system that illuminatesan illuminated surface under a predetermined polarized state with lightfrom a light source includes a polarized state changing device that ispositioned in a light path between the light source and the illuminatedsurface and changes the polarized state of the light that illuminatesthe illuminated surface, and a vertical/horizontal ratio changing devicethat changes a vertical/horizontal ratio of a light intensitydistribution formed on an illumination pupil that is substantially in aFourier transform plane relationship with the illuminated pupil.

According to the ninth embodiment, the polarized state changing deviceincludes a polarized state switching device that changes the polarizedstate of the light that illuminates the illuminated surface between thepredetermined polarized state and a nonpolarized state. In addition,according to the ninth embodiment, the vertical/horizontal ratiochanging device includes an optical element that is positioned at oradjacent to a position that is substantially in the Fourier transformplane relationship with the illumination pupil and has a function tochange a power ratio in two orthogonal directions.

In a tenth embodiment, an exposure apparatus is provided that includesthe illumination optical system of the ninth embodiment and exposes apattern on a mask onto a photosensitive substrate positioned on theilluminated surface.

According to the tenth embodiment, the polarized state changing devicechanges the polarized state of the light in accordance with the patterncharacteristics of the mask, and the vertical/horizontal ratio changingdevice changes the vertical/horizontal ratio of the light intensitydistribution formed on the illumination pupil in accordance with thepattern characteristics of the mask.

In an eleventh embodiment, an exposure method for exposing a pattern ona mask positioned at a first plane onto a photosensitive substratepositioned at a second plane includes a first step that provides lighthaving a predetermined polarization, a second step that illuminates themask with the light provided in the first step, a third step thatexposes the pattern on the mask illuminated in the second step onto thephotosensitive substrate, a fourth step that changes a polarized stateof the light on the second plane, and a fifth step that changes avertical/horizontal ratio of a light intensity distribution formed on anillumination pupil that is substantially in a Fourier transform planerelationship with the second plane.

According to the eleventh embodiment, the fourth step changes thepolarized state of the light in accordance with the patterncharacteristics of the mask. In addition, according to the eleventhembodiment, the fifth step changes the vertical/horizontal ratio of thelight intensity distribution formed on the pupil plane in accordancewith the pattern characteristics of the mask.

In a twelfth embodiment, an illumination optical system that illuminatesan illuminated surface with light from a light source includes apolarized state illumination setting device that sets a polarized stateof the light that illuminates the illuminated surface to a predeterminedpolarized state, and an optical integrator positioned in a light pathbetween the light source and the illuminated surface. The opticalintegrator includes a first one-dimensional cylindrical lens arrayarranged with a pitch along a predetermined first direction and a secondone-dimensional cylindrical lens array arranged with a pitch along asecond direction that crosses the first direction.

According to the twelfth embodiment, the first and secondone-dimensional cylindrical lens arrays are integrally provided with asingle light transmissive substrate. In addition, according to thetwelfth embodiment, the illumination optical system also includes aplurality of cylindrical lens array plates having the first and secondone-dimensional cylindrical lens arrays, and the plurality ofcylindrical lens array plates are positioned with a space from eachother along a direction of an optical axis of the illumination opticalsystem. Furthermore, at least one of the pitch along the first directionof the first one-dimensional cylindrical lens array and the pitch alongthe second direction of the second one-dimensional cylindrical lensarray is equal to or less than 2 mm.

In a thirteenth embodiment, an exposure apparatus includes theillumination optical system of the twelfth preferred embodiment andexposes a pattern on a mask onto a photosensitive substrate positionedon the illuminated surface.

In a fourteenth embodiment, an exposure method includes an illuminationstep that illuminates a mask using the illumination optical system ofthe twelfth embodiment, and an exposure step that exposes a pattern onthe mask onto a photosensitive substrate positioned on the illuminatedsurface.

Exemplary embodiments of this invention are explained with reference tothe attached drawings.

FIG. 1 is a diagram schematically showing a structure of an exposureapparatus equipped with an illumination optical system according to anexemplary embodiment of this invention. In FIG. 1, the Z axis is set ina normal direction of a wafer W, which is a photosensitive substrate.The Y axis is set in a direction on the wafer surface parallel with theplane of FIG. 1. The X axis is set in a direction in the wafer surfaceperpendicular to the plane of the FIG. 1. In addition, in FIG. 1, theillumination optical system is configured to perform annularillumination.

The exposure apparatus of this embodiment is equipped with a laser lightsource 1 for providing exposure light (illumination light). A KrFexcimer laser light source, which provides light with a wavelength of248 nm, or an ArF excimer laser light source, which provides light witha wavelength of 193 nm, for example, may be used as the laser lightsource 1. A light beam with substantially parallel light raysilluminated from the laser light source 1 along the Z direction has arectangular cross section that is elongated in the X direction andenters into a beam expander 2 formed of a pair of lenses 2 a and 2 b.The lenses 2 a and 2 b have negative refractive power and positiverefractive power, respectively, in the plane of FIG. 1 (in the YZplane). Therefore, the light beam that enters into the beam expander 2is expanded in the plane of FIG. 1 and shaped into a light beam that hasa predetermined rectangular cross section.

The light beam with substantially parallel light rays transmittedthrough the beam expander 2, which functions as a shaping opticalsystem, enters to an afocal zoom lens 5 through a phase member 10, adepolarizer (depolarization element) 20, and a diffractive opticalelement 4, after being deflected in the Y direction by a folding mirror3. Structures and functions of the phase member 10 and the depolarizer20 will be described later. In general, the diffractive optical elementis formed by forming steps on a substrate such that the steps have apitch of approximately the wavelength of the exposure light(illumination light), and have a function to diffract the incident lightbeam in a predetermined angle. In detail, the diffractive opticalelement 4 has a function to form a circular light intensity distributionin a far field (or Fraunhofer diffraction region) when a light beam withparallel light rays having a circular cross section enters thediffractive optical element 4.

Therefore, the light beam transmitted through the diffractive opticalelement 4 forms a circular light intensity distribution, that is, alight beam having a circular cross section, at a pupil position of theafocal zoom lens 5. The diffractive optical element 4 is structured tobe removable from the path of the illumination light. The afocal zoomlens 5 is structured such that a magnification can be changedcontinuously in a predetermined range while maintaining an afocal system(afocal optical system). The light beam transmitted through the afocalzoom lens 5 enters a diffractive optical element 6 for annularillumination. The afocal zoom lens 5 connects, with substantiallyoptical conjugation the origin of divergence by the diffractive opticalelement 4 and a diffractive surface of the diffractive optical element6. The numerical aperture of the light beam converged to a point on thediffractive surface or a plane adjacent thereto of the diffractiveoptical element 6 varies depending on the magnification of the afocalzoom lens 5.

The diffractive optical element 6 for annular illumination functions toform a ring-shaped light intensity distribution in a far field thereofwhen a light beam having parallel rays is incident thereto. Thediffractive optical element 6 is structured so as to be insertable intothe path of the illumination light, and replaceable with a diffractiveoptical element 60 for quadrupole illumination, a diffractive opticalelement 61 for circular illumination, a diffractive optical element 62for dipole illumination along the X axis, or a diffractive opticalelement 63 for dipole illumination along the Y axis. Structures andfunctions of the diffractive optical element 60 for quadrupoleillumination, the diffractive optical element 61 for circularillumination, the diffractive optical element 62 for dipole illuminationalong the X axis, or the diffractive optical element 63 for dipoleillumination along the Y axis will be described later.

The light beam transmitted through the diffractive optical element 6enters into a zoom lens 7. Near the rear focal plane of the zoom lens 7,an incident surface of a micro lens array (or a fly's-eye lens) 8 ispositioned. The micro lens array 8 is an optical element formed of manymicro lenses having a positive refractive power arranged densely in amatrix form. In general, a micro lens array is structured by forming amicro lens group by, for example, etching a plane parallel plate.

Each of the micro lenses forming the micro lens array is smaller thaneach of the lens elements structuring a fly's-eye lens. Moreover, in themicro lens array, many micro lenses (micro refractive surfaces) areintegrally formed without being mutually isolated from each other, whichis different from the fly's-eye lens, in which lens elements aremutually isolated from each other. However, the micro lens array is awavefront splitting type optical integrator, which is the same as thefly's-eye lens, in that lens elements having positive refractive powerare arranged in a matrix form.

As described above, the light beam from the circular light intensitydistribution formed at the pupil position of the afocal zoom lens 5through the diffractive optical element 4 enters the diffractive opticalelement 6 as a light beam having various angular components, afterexiting from the afocal zoom lens 5. That is, the diffractive opticalelement 4 forms an optical integrator that functions to form an angularlight beam (a non-parallel light beam having an angular distribution).On the other hand, the diffractive optical element 6 has a function as alight beam conversion element that forms a ring-shaped light intensitydistribution at a far field thereof, when the light beam with parallellight rays enters the diffractive optical element 6. Therefore, thelight beam transmitted through the diffractive optical element 6 formsan annular illumination field about an optical axis AX, for example, inthe rear-side focal plane of zoom lens 7 (therefore, an incident surfaceof the micro lens array 8).

An outer diameter of the annular illumination field formed on theincident surface of the micro lens array 8 varies depending on a focallength of the zoom lens 7. As such, the zoom lens 7 brings thediffractive optical element 6 and the incident surface of the micro lensarray 8 into a substantial Fourier transform relationship. The lightbeam that entered the micro lens array 8 is divided two-dimensionally.Many light sources (hereinafter referred to as “secondary light source”)in an annular shape, which is the same as the illumination field formedby the incident light beam, are formed on the rear focal plane of themicro lens array 8 as shown in FIG. 2A.

The light beam from the annular secondary light sources formed in therear focal plane of the micro lens array 8 superimposingly illuminates amask M, on which a predetermined pattern is formed, after beingconverged by a condenser optical system 9. The light beam transmittedthrough the pattern on the mask M forms an image of the pattern of themask onto a wafer, which is a photosensitive substrate, through aprojection optical system PL. Accordingly, by performing batch or scanexposure while two-dimensionally driving and controlling the wafer W ina plane perpendicular to the optical axis AX of the projection opticalsystem PL (XY plane), the pattern on the mask M is successively exposedin each exposure region of the wafer W.

In this embodiment, even if the magnification of the afocal zoom lens 5is changed, the center height (a distance to a center line of thecircular shape from the optical axis AX) d0 of the annular secondarylight source does not change, but only the width (½ of a differencebetween the outer radius (diameter) and the inner radius (diameter)) w0of the annular secondary light source changes. That is, by changing themagnification of the afocal zoom lens 5, both the size (outer diameter)and the shape (annular ratio: inner diameter/outer diameter) of theannular secondary light source may be changed.

Furthermore, if the focal length of the zoom lens 7 is changed, thecenter height d0 and the width w0 of the annular secondary light sourceare both changed without the annular ratio being changed. That is, bychanging the focal length of the zoom lens 7, the outer diameter of theannular secondary light source may be changed without the annular ratiothereof being changed. Accordingly, in this embodiment, by appropriatelychanging the magnification of the afocal zoom lens 5 and the focallength of the zoom lens 7, only the annular ratio of the annularsecondary light source may be changed without changing the outerdiameter thereof.

Moreover, quadrupole illumination can be achieved by setting thediffractive optical element 60, instead of the diffractive opticalelement 6, in the illumination light path. The diffractive opticalelement 60 for quadrupole illumination has a function to form aquadruple light intensity distribution in the far field thereof, whenthe light beam with parallel light rays enters it. Therefore, the lightbeam transmitted through the diffractive optical element 60 forms on theincident surface of the micro lens array 8 a quadrupole illuminationfield comprised of four disc-shaped illumination fields around theoptical axis, for example. As a result, as shown in FIG. 2B, aquadrupole secondary light source, which is the same as the illuminationfield formed on the incident surface of the micro lens array 8, also isformed in the rear focal plane of the micro lens array 8.

Similar to the case of annular illumination, in quadrupole illumination,by changing the magnification of the afocal zoom lens 5, both the outerdiameter (diameter of a circle circumscribing the four disc-shapedplanar light sources) Do and the annular ratio (a diameter Di of acircle inscribing the four disc-shaped planar light sources/a diameterDo of the circle circumscribing the four disc-shaped planar lightsources) of the quadrupole secondary light sources can be changed. Inaddition, by changing the focal length of the zoom lens 7, the outerdiameter of the quadrupole light source can be changed without changingthe annular ratio thereof. As a result, by appropriately changing themagnification of the afocal zoom lens 5 and the focal length of the zoomlens 7, only the annular ratio of the quadrupole secondary light sourcemay be changed without changing the outer diameter thereof.

Moreover, by removing the diffractive optical element 4 from theillumination light path and setting the diffractive optical element 61for circular illumination, instead of the diffractive optical element 6or 60, in the illumination light path, normal circular illumination maybe achieved. In this case, the light beam having a rectangular crosssection enters the afocal zoom lens 5 along the optical axis AX. Thelight beam that enters the afocal zoom lens 5 is expanded or reduced inaccordance with the magnification thereof. The light beam then exitsfrom the afocal zoom lens 5 along the optical axis AX while maintainingthe rectangular cross section, and enters the diffractive opticalelement 61.

The diffractive optical element 61 for circular illumination has,similar to the diffractive optical element 4, a function to form acircular light intensity distribution in the far field thereof, when thelight beam with parallel light rays having the rectangular cross sectionenters it. Therefore, the circular light beam formed by the diffractiveoptical element 61 forms a circular illumination field about the opticalaxis AX in the incident surface of the micro lens array 8. As a result,a circular secondary light source centered about the optical axis AXalso is formed in the rear focal plane of the micro lens array 8. Inthis case, by changing the magnification of the afocal zoom lens 5 andthe focal length of the zoom lens 7, the outer diameter of the circularsecondary light source can be appropriately changed.

Moreover, dipole illumination in the X direction may be achieved bysetting the diffractive optical element 62 in the illumination lightpath, instead of the diffractive optical elements 6, 60 or 61. Thediffractive optical element 62 for dipole illumination in the Xdirection functions to form a dipole light intensity distribution withillumination fields spaced apart along the X direction in the far fieldthereof when the light beam with parallel light rays enters it.Therefore, the light beam transmitted through the diffractive opticalelement 62 forms on the incident surface of the micro lens array 8 adipole illumination field formed of two circular illumination fieldsabout the optical axis AX, which are spaced apart along the X direction,for example. As such, as shown in FIG. 3A, the dipole secondary lightsource formed along the X direction, which is the same as theillumination fields formed on the incident surface of the micro lensarray 8, also is formed on the rear-side focal plane of the micro lensarray 8.

Furthermore, dipole illumination in the Y direction may be achieved bysetting the diffractive optical element 63 in the illumination lightpath, instead of the diffractive optical element 6, 60, 61 or 62. Thediffractive optical element 63 for the dipole illumination in the Ydirection functions to form a dipole light intensity distribution withilluminated fields spaced apart in the Z direction (corresponding to theY direction on the mask and the wafer), in the far field thereof whenthe light beam with parallel light rays enters it. Therefore, the lightbeam transmitted through the diffractive optical element 63 forms on theincident surface of the micro lens array 8 a dipole illumination fieldformed of the two circular illumination fields spaced apart along the Zdirection, about the optical axis AX, for example. As such, as shown inFIG. 3B, the dipole secondary light source formed along the Z direction,which is the same as the illumination fields formed on the incidentsurface of the micro lens array 8, also is formed on the rear-side focalplane of the micro lens array 8.

Similar to the case of the quadrupole illumination, in the dipoleillumination, by changing the magnification of the afocal zoom lens 5,both the outer diameter (diameter of a circle circumscribing the twodisc-shaped planar light sources) Do and the annular ratio (a diameterDi of a circle inscribing the two disc-shaped planar light sources/adiameter Do of the circle circumscribing the two disc-shaped planarlight sources) of the dipole secondary light sources may be changed. Inaddition, by changing the focal length of the zoom lens 7, the outerdiameter of the dipole light source may be changed without the annularratio thereof being changed. As a result, by appropriately changing themagnification of the afocal zoom lens 5 and the focal length of the zoomlens 7, only the annular ratio of the dipole secondary light source maybe changed without changing the outer diameter thereof.

FIG. 4 is a diagram schematically showing a structure of the phasemember and the depolarizer shown in FIG. 1. Referring to FIG. 1, thephase member 10 is formed from a half-wave plate, structured so that itscrystal optic axis is rotatable about the optical axis AX. Thedepolarizer is formed from a wedge crystal prism 20 a and a wedge silicaprism 20 b, which has a complimentary shape to the crystal prism 20 a.As an integral prism assembly, the crystal prism 20 a and the silicaprism 20 b are structured to be removable from the illumination lightpath. When using a KrF excimer laser light source or an ArF excimerlaser light source as the laser light source 1, substantially linearlypolarized light enters into the half-wave plate 10 because the lightejected from these light sources typically has a degree of polarizationof 95% or more.

If the crystal optic axis of the half-wave plate 10 is configured toform an angle of 0 or 90 degrees with respect to a polarization plane ofthe incident linearly polarized light, the linearly polarized light thatenters the half-wave plate is transmitted through the half-wave plate 10as is, without changing its polarization plane. If the crystal opticaxis of the half-wave plate 10 is configured to form an angle of 45degrees with respect to a polarization plane of the incident linearlypolarized light, the linearly polarized light that enters the half-waveplate 10 is converted to linearly polarized light in which thepolarization plane is changed by 90 degrees. Furthermore, if the crystaloptic axis of the crystal prism 20 a is configured to form an angle of45 degrees with respect to a polarization plane of the incident linearlypolarized light, the linearly polarized light that enters the crystalprism 20 a is converted into light having a nonpolarized state(nonpolarized light).

In this embodiment, the crystal optic axis of the crystal prism 20 a isconfigured to form an angle of 45 degrees with respect to a polarizationplane of the incident linearly polarized light when the depolarizer 20is positioned in the illumination light path. If the crystal optic axisof the crystal prism 20 a is configured to form an angle of 0 or 90degrees with respect to a polarization plane of the incident linearlypolarized light, the linearly polarized light that enters the crystalprism 20 a is transmitted through the crystal prism 20 a as is, withoutchanging its polarization plane. Moreover, if the crystal optic axis ofthe half-wave plate 10 is configured to form an angle of 22.5 degreeswith respect to a polarization plane of the incident linearly polarizedlight, the linearly polarized light that enters the half-wave plate 10is converted to light having a nonpolarized state that includes alinearly polarized component, by which the light is transmitted throughthe half-wave plate 10 without changing its polarization plane, and alinearly polarized component by which the polarization plane is changeby 90 degrees.

As described above, in this embodiment, the linearly polarized lightfrom the laser light source 1 enters the half-wave plate 10. To simplifyexplanations described below, it is assumed that P-polarized light(linearly polarized light having a polarization plane in the Z directionat the position of the half-wave plate in FIG. 1; hereinafter referredto as “polarized in Z direction”) enters the half-wave plate 10. Whenthe depolarizer 20 is positioned in the illumination light path, if thecrystal optic axis of the half-wave plate 10 is configured to form anangle of 0 or 90 degrees with respect to a polarization plane of theincident P-polarized light (polarized in the Z direction), theP-polarized light that enters the half-wave plate 10 is transmittedthrough the half-wave plate 10 as is and enters the crystal prism 20 awithout changing its polarization plane. Because the crystal optic axisof the crystal prism 20 a is configured to form an angle of 45 degreeswith respect to a polarization plane of the incident P-polarized light(polarized in the Z direction), the P-polarized light (light polarizedin the Z direction) that enters the crystal prism 20 a is converted intolight having a nonpolarized state (a depolarized state).

The nonpolarized light transmitted through the crystal prism 20 ailluminates the mask M (and therefore the wafer W) in the nonpolarizedstate through the silica prism 20 b, which functions as a compensator tocompensate in the traveling direction of the light. On the other hand,if the crystal optic axis of the half-wave plate 10 is configured toform an angle of 45 degrees with respect to a polarization plane of theincident P-polarized light, the polarization plane for the P-polarizedlight (polarized in the Z direction) that enters the half-wave plate 10is changed by 90 degrees and enters the crystal prism 20 a asS-polarized light (linearly polarized light having a polarization planein the X direction at the position of the half-wave plate in FIG. 1;hereinafter referred to as “polarized in the X direction”). Because thecrystal optic axis of the crystal prism 20 a is also configured to forman angle of 45 degrees with respect to a polarization plane of theincident S-polarized light (polarized in the X direction), theS-polarized (polarized in the X direction) light that enters the crystalprism 20 a is converted into nonpolarized light and illuminates the maskM in the nonpolarized state through the silica prism 20 b.

On the other hand, when the depolarizer 20 is removed from theillumination light path, if the crystal optic axis of the half-waveplate is configured to form an angle of 0 or 90 degrees with respect toa polarization plane of the incident P-polarized light (polarized in theZ direction), the P-polarized (polarized in the Z direction) light thatenters the half-wave plate 10 is transmitted through the half-wave plate10 as is as P-polarized light (polarized in the Z direction) without itspolarization plane being changed. Therefore, the mask M is illuminatedby the P-polarized light (polarized in the Z direction). If the crystaloptic axis of the half-wave plate 10 is configured to form an angle of45 degrees with respect to a polarization plane of the incidentP-polarized light (polarized in the Z direction), the P-polarized lightthat enters the half-wave plate 10 becomes S-polarized light as itspolarization plane is changed by 90 degrees, and the mask M isilluminated with the S-polarized light (polarized in the X direction).

As described above, according to this invention, the mask M can beilluminated in a nonpolarized state by positioning the depolarizer 20 inthe illumination light path. The mask M may be illuminated in aP-polarized state (polarized in the Y direction) by removing thedepolarizer 20 from the illumination light path and setting the crystaloptic axis of the half-wave plate 10 to form an angle of 0 or 90 degreeswith respect to a polarization plane of the incident P-polarized light(polarized in the Z direction). The mask M may be illuminated in theS-polarized state (polarized in the X direction) by removing thedepolarizer 20 from the illumination light path and setting the crystaloptic axis of the half-wave plate 10 to form an angle of 45 degrees withrespect to a polarization plane of the incident P-polarized light(polarized in the Z direction).

In other words, in this embodiment, with the operations of the polarizedstate switching device that is composed of the half-wave plate 10 andthe depolarizer 20, the polarized state for the light that illuminatesthe mask (and therefore the wafer W), which has a surface to beilluminated, may be switched between the linearly polarized state andthe nonpolarized state. In addition, the polarized state may be switchedbetween the P-polarized state and the S-polarized state (between thepolarized states that are perpendicular to each other) (polarizationplanes for the linearly polarized light may be varied) when illuminatingthe mask M with the linearly polarized light. As a result, in thisembodiment, appropriate illumination conditions can be achieved bychanging the polarized state for the illumination light whilecontrolling the loss of light amount in accordance with thecharacteristics of the patterns on the mask M. Therefore, the wafer Wcan be exposed well under an appropriate illumination condition achievedin accordance with the characteristics of the pattern on the mask M. Inparticular, when illuminating the mask M with the linearly polarizedlight, the linearly polarized light from the light source 1 may bedirected to the illuminated surface using the polarized state switchingdevice without substantially losing the light amount.

In detail, by setting to the dipole illumination in the X direction, forexample, and by illuminating the mask with the light in the linearlypolarized state having the polarization plane along the X direction onthe mask M, a pattern having extremely narrow line widths in the Xdirection may be accurately exposed onto a critical layer on the waferW. Subsequently, by switching to the dipole illumination in the Xdirection, for example, and by illuminating the mask M with the linearlypolarized light that has the polarization plane along the Y direction onthe mask M, a pattern having extremely narrow line widths in the Ydirection may be accurately exposed onto the critical layer on the waferW.

Furthermore, after completing the double exposure on the critical layer,a two-dimensional pattern that has relatively wide line widths may beexposed on the non-critical layer (middle layer or rough layer) on thewafer W at a high throughput by, for example, maintaining the dipoleillumination, or by switching to the quadrupole, annular, or circularillumination and illuminating the mask with light in the nonpolarizedstate. However, these are only examples. In general, the wafer W may beexposed well under appropriate illumination conditions by setting thesecondary light source at an appropriate shape and size and setting thelight that illuminates the mask M in an appropriate polarized state inaccordance with the characteristics of the pattern on the mask M.

For practical purposes, scattering of light on a resist layer formed onthe wafer W differs when the P-polarized light beam is diagonallyincident on the wafer W and when the S-polarized light beam isdiagonally incident on the wafer W. In detail, the S-polarized light hashigher reflectivity than the P-polarized light so that the P-polarizedlight beam reaches deeper inside the resist layer than the S-polarizedlight beam. By using such a difference in the optical characteristics ofthe P-polarized light and the S-polarized light with respect to theresist layer, and by achieving appropriate illumination conditions bychanging the polarized state for the illumination light in accordancewith the characteristics of the pattern on the mask M, the wafer W maybe exposed well under appropriate illumination conditions.

In the above-described embodiment, the half-wave plate 10, which is aphase member for changing the polarization plane of the incidentlinearly polarized light as needed, is positioned on the light sourceside, and the depolarizer 20, which unpolarizes the incident linearlypolarized light as need, is positioned on the mask side. However, theyare not limited to this arrangement, and the same optical functions andeffects may be obtained even if the depolarizer 20 is positioned on thelight source side, and the half-wave plate 10 is positioned on the maskside.

Moreover, in the above-described embodiment, the silica prism 20 b isused as a compensator to compensate the traveling direction of the lighttransmitted through the crystal prism 20 a. However, the invention isnot limited to this, and a wedge-shaped prism may be formed by anoptical material, such as quartz or fluorite, which has high durabilitywith respect to the KrF excimer laser beam or the ArF excimer laserbeam. This applies similarly in other related exemplary modifications.

FIG. 5 is a diagram schematically showing a structure of a polarizedstate switching device according to a first exemplary modification. Thepolarized state switching device according to the first modificationshown in FIG. 5 has a structure similar to that of the polarized stateswitching device according to the embodiment shown in FIG. 4. However,in contrast with the embodiment in FIG. 4, in which the depolarizer 20is structured to be removable from the illumination light path, thefirst exemplary modification in FIG. 5 is basically different in thatthe crystal prism 20 a and the silica prism 20 b, which together formthe depolarizer 20, are structured to be integrally rotatable about theoptical axis AX, and that the crystal optic axis of the crystal prism 20a is structured to be rotatable about the optical axis AX. The firstexemplary modification shown in FIG. 5 is explained below, focusing onthe differences from the embodiment shown in FIG. 4.

In the first exemplary modification, if the crystal optic axis of thehalf-wave plate 10 is set to form an angle of 45 degrees with respect toa polarization plane of the incident P-polarized light (polarized in theZ direction), the P-polarized light (polarized in the Z direction) thatenters the half-wave plate 10 is transmitted through the half-wave plate10 and enters the crystal prism 20 a as is in P-polarization (polarizedin the Z direction) without changing the polarization plane of thelight. At this time, if the crystal optic axis of the crystal prism 20 ais set to form an angle of 45 degrees with respect to a polarizationplane of the incident P-polarized light (polarized in the Z direction),the P-polarized light (polarized in the Z direction) that enters thecrystal prism 20 a is converted into light in the nonpolarized state,and the mask M is illuminated by the light in the nonpolarized statethat is transmitted through the quartz prism 20 a. Moreover, if thecrystal optic axis of the crystal prism 20 a is set to form an angle of0 or 90 degrees with respect to a polarization plane of the incidentP-polarized light (polarized in the Z direction), the P-polarized light(polarized in the Z direction) that enters the crystal prism 20 a istransmitted through the crystal prism 20 a as P-polarized light withoutchanging the polarization plane, and the mask M is illuminated by thelight in the P-polarized state (polarized in the Y direction) that istransmitted through the quartz prism 20 a.

On the other hand, if the crystal optic axis of the half-wave plate 10is set to form an angle of 45 degrees with respect to a polarizationplane of the incident P-polarized light, the polarization plane for theP-polarized light (polarized in the Z direction) that enters thehalf-wave plate 10 changes by 90 degrees and enters the crystal prism 20a as it becomes the S-polarized light (polarized in the X direction). Atthis time, if the crystal optic axis of the crystal prism 20 a is set toform an angle of 45 degrees with respect to a polarization plane of theincident P-polarized light (polarized in the Z direction), theS-polarized light (polarized in the X direction) that enters the crystalprism 20 a is converted into light in the nonpolarized state andilluminates the mask M in the nonpolarized state through the silicaprism 20 b. If the crystal optic axis of the crystal prism 20 a is setto form an angle of 0 or 90 degrees with respect to a polarization planeof the incident S-polarized light (polarized in the X direction), theS-polarized light (polarized in the X direction) that enters the crystalprism 20 a is transmitted as is as S-polarized light (polarized in the Xdirection) without the polarization plane being changed and illuminatesthe mask as S-polarized light (polarized in the X direction) through thesilica prism 20 b.

As described above, in the first exemplary modification of FIG. 5, thepolarized state for the light that illuminates the mask is changedbetween the linearly polarized state and the nonpolarized state bycombining the rotation of the half-wave plate 10 about the optical axisAX and the rotation of the crystal prism 20 a about the optical axis AX.When illuminating the mask M with the linearly polarized light, thepolarized state may be changed between the P-polarized state and theS-polarized state. Moreover, the half-wave plate 10 and the depolarizer20 are also positioned on the light source side and the mask side,respectively, in the first exemplary modification shown in FIG. 5. Thesame optical effects and functions may be achieved by positioning thedepolarizer 20 and the half-wave plate 10 on the light source side andthe mask side, respectively.

FIG. 6 is a diagram schematically showing a polarized state switchingdevice according to a second exemplary modification. The polarized stateswitching device according to the second modification shown in FIG. 6has a structure similar to that of the polarized state switching deviceaccording to the embodiment shown in FIG. 4. However, in contrast withthe embodiment in FIG. 4, in which the depolarizer 20 is structured tobe removable from the illumination light path, the second exemplarymodification shown in FIG. 6 is basically different in that thedepolarizer 20 is fixedly positioned in the illumination light path. Thesecond exemplary modification shown in FIG. 6 is explained below,focusing on the differences from the embodiment shown in FIG. 4.

In the second exemplary modification, the crystal optic axis of thecrystal prism 20 a is positioned to form an angle of 0 or 90 degreeswith respect to a polarization plane of the incident P-polarized light(polarized in the Z direction). Therefore, if the crystal optic axis ofthe half-wave plate 10 is set to form an angle of 0 or 90 degrees withrespect to a polarization plane of the incident P-polarized light(polarized in the Z direction), the P-polarized light (polarized in theZ direction) that enters the half-wave plate 10 is transmitted throughthe half-wave plate 10 as is as P-polarized light (polarized in the Zdirection) and enters the crystal prism 20 a, without its polarizationplane being changed. Because the crystal optic axis of the crystal prism20 a is fixedly positioned to form an angle of 0 or 90 degrees withrespect to a polarization plane of the incident P-polarized light(polarized in the Z direction), the P-polarized light (polarized in theZ direction) that enters the crystal prism 20 a is transmitted throughthe crystal prism 20 a as is as P-polarized light (polarized in the Zdirection) without changing the angle of the polarization plane, andilluminates the mask M as P polarized light (polarized in the Ydirection) through the silica prism 20 b.

Moreover, if the crystal optic axis of the half-wave plate 10 is set toform an angle of 0 or 90 degrees with respect to a polarization plane ofthe incident P-polarized light (polarized in the Z direction), thepolarization plane for the P-polarized light (polarized in the Zdirection) that enters the half-wave plate 10 is changed by 90 degrees,and the light enters the crystal prism 20 a as S-polarized light(polarized in the X direction). Because the crystal optic axis of thecrystal prism 20 a is positioned to form an angle of 0 or 90 degreeswith respect also to a polarization plane of the incident S-polarizedlight (polarized in the X direction), the S-polarized light (polarizedin the X direction) that enters the crystal prism 20 a is transmittedthrough the crystal prism 20 a as is as S-polarized light (polarized inthe X direction) without changing the angle of the polarization planeand illuminates the mask M as S-polarized light (polarized in the Xdirection) through the silica prism 20 b.

Further, if the crystal optic axis of the half-wave plate 10 is set toform an angle of 22.5 degrees with respect to a polarization plane ofthe incident P-polarized light (polarized in the Z direction), thepolarization plane for the P-polarized light that enters the half-waveplate 10 enters the crystal prism 20 a after being converted into lightin the nonpolarized state that includes a P-polarized component(polarized in the Z direction), in which the polarization plane for thelight transmitted as is without any change, and an S-polarized component(polarized in the X direction), in which the angle of the polarizationplane is changed by 90 degrees. Because the crystal optic axis of thecrystal prism 20 a is positioned to form an angle of 0 or 90 degreeswith respect also to the polarization plane of the incident P-polarizedcomponent as well as to the polarization plane of the incidentS-polarized light (polarized in the X direction), the P-polarized light(polarized in the Z direction) and the S-polarized light (polarized inthe X direction) that enters the crystal prism 20 a are transmittedthrough the crystal prism 20 a as is without changing the angle of thepolarization plane and illuminate the mask M in the nonpolarized statethrough the silica prism 20 b.

As described above, in the second exemplary modification shown in FIG.6, by appropriately rotating the half-wave plate 10 about the opticalaxis AX with the depolarizer 20 being fixedly positioned in theillumination light path, the polarized state for the light thatilluminates the mask M may be switched between the linearly polarizedstate and the nonpolarized state, and if illuminating the mask with thelinearly polarized light, the polarized state may be changed between theP-polarized state and the S-polarized state. In addition, in the secondexemplary modification shown in FIG. 6, the half-wave plate 10 and thedepolarizer 20 are also positioned on the light source side and the maskside, respectively. However, the same optical functions and effects maybe obtained even if the depolarizer 20 is positioned on the light sourceside, and the half-wave plate 10 is positioned on the mask side.

FIG. 7 is a diagram schematically showing a structure of a polarizedstate switching device according to a third exemplary modification. Thepolarized state switching device according to the third exemplarymodification shown in FIG. 7 has a structure similar to the polarizedstate switching device according to the first exemplary modificationshown in FIG. 5. However, in contrast with the first exemplarymodification in FIG. 5, in which the polarized state switching device isstructured from the half-wave plate 10 and the depolarizer 20, the thirdexemplary modification shown in FIG. 7 is basically different in thatthe polarized state switching device is structured from only thedepolarizer 20 that is rotatable about the optical axis AX. The thirdexemplary modification shown in FIG. 7 is explained below, focusing onthe differences from the first exemplary modification shown in FIG. 5.

In the third exemplary modification, if the crystal optic axis of thecrystal prism 20 a is set to form an angle of 45 degrees with respect toa polarization plane of the incident P-polarized light (polarized in theZ direction), the P-polarized light that enters the crystal prism 20 ais converted into light in the nonpolarized light and illuminates themask M in the nonpolarized state through the silica prism 20 b. On theother hand, if the crystal optic axis of the crystal prism 20 a is setto form an angle of 0 or 90 degrees with respect to a polarization planeof the incident P-polarized light (polarized in the Z direction), theP-polarized light (polarized in the Z direction) that enters the crystalprism 20 a is transmitted through the crystal prism 20 a as is asP-polarized light (polarized in the Z direction) without changing thepolarization plane and illuminates the mask M in the P-polarized state(polarized in the Y direction) through the silica prism 20 b.

As described above, in the third exemplary modification shown in FIG. 7,by appropriately rotating the crystal prism 20 a about the optical axisAX, the polarized state for the light that illuminates the mask M may beswitched between the linearly polarized state and the nonpolarizedstate. Moreover, in the third exemplary modification shown in FIG. 7,the same optical operational effects may be obtained by structuring thedepolarizer 20 to be rotatable about the optical axis AX and removablefrom the illumination light path and by setting the depolarizer 20 to beremoved from the illumination light path to allow illumination of themask M in the P-polarized state.

FIG. 8 is a diagram schematically showing a structure of the depolarizeraccording to an exemplary modification. In the above-describedembodiment and first-third exemplary modifications, the depolarizer 20adapts a structure having the crystal prism 20 a. However, as shown inthe exemplary modification shown in FIG. 8, the depolarizer 21 may bestructured from a polarized beam splitter 21 a and a reflection system(21 b-21 e). According to FIG. 8, the depolarizer 21 is equipped withthe polarized beam splitter 21 a positioned in the illumination lightpath. Of the light that enters the polarized beam splitter 21 a, theP-polarized light (polarization directions indicated by bidirectionalarrows in the figure) with respect to a polarization separation surfaceof the polarized beam splitter 21 a is transmitted through the polarizedbeam splitter 21 a.

On the other hand, the S-polarized light (polarization directionindicated by dots in the figure) with respect to the polarizationseparation surface of the polarized beam splitter 21 a is, after beingreflected by the polarized beam splitter 21 a, returned to the polarizedbeam splitter 21 a as light that has been reflected four times in aplane parallel to the surface of FIG. 8 by actions of the reflectionsystem structured from four reflection mirrors 21 b-21 e. The reflectionsystem (21 b-21 e) is structured such that the path of the P-polarizedlight that is transmitted through the polarized beam splitter 21 a andthe path of the S-polarized light that is eventually reflected by thepolarized beam splitter 21 a substantially match each other. As aresult, the P-polarized light that is transmitted through the polarizedbeam splitter 21 a and the S-polarized light that is eventuallyreflected by the polarized beam splitter 21 a are ejected from thedepolarizer 21 substantially on the same light path. However, theS-polarized light is delayed compared to the P-polarized light by thelength of the light path created by the reflection system (21 b-21 e).

The depolarizer 21 structured from the polarized beam splitter 21 a andthe reflection system (21 b-21 e) has optical functions that arebasically equivalent to those of the depolarizer 20 structured from thecrystal prism 20 a and the silica prism 20 b. Therefore, the depolarizer20 in the exemplary embodiment and the first to third exemplarymodifications may be replaced with the depolarizer 21 according to theexemplary modification shown in FIG. 8. That is, when using thedepolarizer 21 in the exemplary embodiment shown in FIG. 4, thepolarized beam splitter 21 a and the reflection system (21 b-21 e) maybe structured to be integrally insertable into and removable from theillumination light path.

When using the depolarizer 21 in the first exemplary modification shownin FIG. 5 or the third exemplary modification shown in FIG. 7, thepolarized beam splitter 21 a and the reflection system (21 b-21 e) maybe structured to be integrally rotatable about the optical axis AX.Furthermore, when using the depolarizer 21 in the second exemplarymodification shown in FIG. 6, the polarized beam splitter 21 a and thereflection system (21 b-21 e) may be positioned fixedly in theillumination light path.

By using the depolarizer 21 according to the exemplary embodiment shownin FIG. 8, the coherency of the laser beam that illuminates the mask Mmay be reduced, and therefore, a speckle contrast on the wafer may bereduced, by setting the length of the light path on the reflectionsystem (21 b-21 e) substantially longer than a coherence length.Detailed structures of and various examples of modifications for adepolarizer, which has a polarized beam splitter and a reflection systemand are adaptable in this invention, are described in Japanese Laid-OpenPatent Application No. 11-174365, Japanese Laid-Open Patent ApplicationNo. 11-312631, Japanese Laid-Open Patent Application No. 2000-223396 andU.S. Pat. No. 6,238,063. The disclosure of U.S. Pat. No. 6,238,063 isincorporated herein by reference in its entirety.

FIG. 9 is a diagram schematically showing an internal structure for abeam matching unit positioned between the light source and the polarizedstate switching device shown in FIG. 1. In the beam matching unit BMUshown in FIG. 9, the beam with parallel light rays provided from thelaser light source 1 (e.g., KrF excimer laser light source or ArFexcimer laser light source) enters the beam expander 2 after beingtransmitted through a pair of deviation prisms 31 and a plane parallelplate 32. The laser light source 1 may be provided on a base plate A ona lower level, for example.

One of the pair of deviation prisms 31 is structured to be rotatableabout the optical axis AX. Therefore, by relatively rotating the pair ofdeviation prisms 31 about the optical axis AX, the angle of the beamwith parallel light rays with respect to the optical axis AX may beadjusted. That is, the pair of deviation prisms 31 forms a beam angleadjustment device for adjusting an angle of the beam with parallel lightrays provided from the laser light source 1 with respect to the opticalaxis AX. In addition, the plane parallel plate 32 is structured to berotatable about two axes that are orthogonal to each other and thatextend in a plane perpendicular to the optical axis AX.

Accordingly, by rotating the plane parallel plate 32 about each of theaxes to incline the plane parallel plate 32 with respect to the opticalaxis AX, the beam with parallel light rays can be moved in parallel tothe optical axis AX. That is, the plane parallel plate 32 forms a beamparallel movement device for moving the beam with parallel light raysprovided from the laser light source 1 in parallel to the optical axisAX. As a result, the beam with parallel light rays from the light source1, which is transmitted through the pair of deviation prisms 31 and theplane parallel plate 32, enters a first rectangular prism 33 after beingexpanded and formed into a beam with parallel light rays having apredetermined cross-sectional shape through the beam expander 2.

The beam with parallel light rays deflected in a vertical direction bythe first rectangular prism 33, which functions as a back surfacereflection mirror, enters a sixth rectangular prism 38 as a beam withparallel light rays after passing through an opening on the base plate Bon an upper level, after being sequentially reflected by the secondrectangular prism 34 to the fifth rectangular prism 37, which alsofunction as back surface reflection mirrors. As shown in FIG. 9, thesecond rectangular prism 34 to the fifth rectangular prism 37 arearranged in such a manner that the beam with parallel light raysdeflected in the vertical direction by the first rectangular prism 33 tobe directed to the sixth rectangular prism is transmitted around pipes39 for supplying pure water or ventilating air, for example.

The beam deflected in a horizontal direction by the sixth rectangularprism 38, which functions as a back side reflection mirror, enters ahalf mirror 40. The beam reflected by the half mirror 40 is lead to adisplacement and inclination detection system 41. On the other hand, thebeam transmitted through the half mirror 40 is lead to a polarized stateswitching device 42 formed by the half-wave plate 10 and the depolarizer20. By the displacement and inclination detection system 41,displacement and inclination of the beam with parallel light rays thatenters the polarized state switching device 42 (and subsequently thediffractive optical element 4, which functions as an opticalintegrator), is detected with respect to the optical axis AX.

If, for example, the ArF excimer laser light source is used as the laserlight source 1, it is generally the case that a required durability issecured for light transmissive members that receive illumination oflight having high energy density by using fluorite for those members. Inthis case, as described below, the polarization plane for the linearlypolarized light may change in a short or long term when the light istransmitted through the light transmissive members formed by fluorite.If the polarization plane for the linearly polarized light is changed bythe light transmissive members formed by fluorite, the crystal prism 20a does not function as the nonpolarized element.

FIG. 10 is a diagram explaining the crystal orientation of fluorite. Asshown in FIG. 10, the crystal orientation of fluorite is described withreference to the cubic crystal axes a₁, a₂ and a₃. That is, crystalorientations [100], [010] and [001] are provided along the orientationaxes +a₁, +a₂ and +a₃, respectively. In addition, a crystal orientation[101] is provided in a direction extending 45 degrees from the crystalorientations [100] and [001] in the a₂a₃ plane. A crystal orientation[110] is provided in a direction extending 45 degrees from the crystalorientations [100] and [010] in the a₁a₂ plane. A crystal orientation[011] is provided in a direction extending 45 degrees from the crystalorientations [010] and [001] in the a₂a₃ plane. Furthermore, a crystalorientation [111] is provided in a direction forming equivalent acuteangles with respect to the crystal axes +a₁, +a₂ and +a₃. In FIG. 10,only crystal orientations in a space are provided by the crystal axes+a₁, +a₂ and +a₃. However, similar crystal orientations may be providedin other spaces.

As verified by applicants, the polarization plane for the linearlypolarized light is not substantially changed by the light transmissivemembers formed by fluorite as long as the traveling direction of thelight is substantially matched with the crystal orientation [111] or acrystal orientation equivalent thereto in the crystal structure.Similarly, the polarization plane for the linearly polarized light isnot substantially changed by the light transmissive members formed byfluorite as long as the traveling direction of the light issubstantially matched with the crystal orientation [100] or a crystalorientation equivalent thereto in the crystal structure. On the otherhand, if the traveling direction of the light is substantially matchedwith the crystal orientation [110] or a crystal orientation equivalentthereto in the crystal structure, the polarization plane for thelinearly polarized light is changed through the light transmissivemember formed by fluorite in a short or long term.

In this specification, “a crystal orientation equivalent to a certaincrystal orientation in the crystal structure” device a crystalorientation equivalent in the crystal structure to a crystal orientationin which indexes for the crystal orientation is reordered and in whichsigns for at least a part of the indexes are reversed, that is, when thecrystal orientation is [uvw], then equivalent orientations are [uwv],[vuw], [vwu], [wuv], [wvu], [−uvw], [−uwv], [−vuw], [−vwu], [−wuv],[−wvu], [u−vw], [u−wv], [v−uw], [v−wu], [w−uv], [w−vu], [uv−w], [uw−v],[vu−w], [vw−u], [wu−v], [wv−u], [−u−vw], [−u−wv], [−uv−w], [−uw−v],[−v−uw], [−v−wu], [−vu−w], [−vw−u], [−w−uv], [−w−vu], [−wu−v], [−wv−u],[u−v−w], [u−w−v], [v−u−w], [v−w−u], [w−u−v], [w−v−u], [−u−v−w],[−u−w−v], [−v−u−w], [−v−w−u], [−w−u−v], and [−w−v−u]. Moreover, in thisspecification, the crystal orientation [uvw] and the crystalorientations equivalent to the crystal orientation [uvw] in the crystalstructure is referred to as a crystal orientation <uvw>. Furthermore, aplane orthogonal to the crystal orientation [uvw] and the crystalorientation equivalent to the crystal orientation [uvw] in the crystalstructure, is referred to as a crystal plane (uvw), and a crystal planeequivalent to the crystal plane (uvw) in the crystal structure isreferred to as a crystal plane {uvw}.

In this exemplary embodiment, the traveling direction of the light isconfigured to be closer to the crystal orientations <111> and <100> thanto the crystal orientation <110> in the light transmissive member formedby fluorite that is positioned in the light path between the laser lightsource 1 and the polarized state switching device 42. In detail, if theoptical member, such as lens components (2 a, 2 b) that form the beamexpander 2, securely positioned in the light path is formed by fluorite,the optical axis of the optical member is configured to substantiallymatch the crystal orientation <111> or <100>.

In this case, because the laser light is transmitted substantially alongthe crystal orientation <111> or <100>, the polarization plane for thelinearly polarized light that is transmitted through the lens components(2 a, 2 b) is not changed substantially. Similarly, if the pair ofdeviation prisms 31 is formed by fluorite, changes in the polarizationplane for the transmitted linearly polarized light may be substantiallyavoided by configuring the optical axis of the pair of the deviationprisms 31 substantially match the crystal orientation <111> or <100>.

Moreover, if the rectangular prisms 33-38, which function as backsurface reflection mirrors, are formed by fluorite, an incident surfaceand an exit surface of the rectangular prisms 33-38 are configured tosubstantially match the crystal plane {100}, and reflection surfaces ofthe rectangular prisms 33-38 are configured to substantially match thecrystal plane {110}. In such a case, because the laser beam istransmitted substantially along the crystal orientation <100>, thepolarization plane for the linearly polarized light transmitted throughthe rectangular prisms 33-38 does not substantially change.

Furthermore, if the plane parallel plate 32, which functions as the beamparallel movement device, that is provided in the light path inclineablywith respect to the optical axis AX and that moves in parallel the lightbeam incident along the optical axis AX, is formed by fluorite, theoptical axis of the plane parallel plate 32 is configured tosubstantially match with the crystal orientation <100>. This is becausethe crystal orientations <100> and <110> form an angle of 45 degrees,while the crystal orientations <111> and <110> form an angle of about 35degrees.

If the optical axis of the plane parallel plate 32 is substantiallymatched with the crystal orientation <111>, that is, substantiallymatched with the crystal plane {111} of the optical plane thereof, thetraveling direction of the laser light transmitted through the planeparallel plate 32 comes close to the crystal orientation <110> when theplane parallel plate 32 is inclined at the maximum level (e.g., about 32degrees) with respect to the optical axis AX. However, if the opticalaxis of the plane parallel plate 32 is substantially matched with thecrystal orientation <100>, that is, if the optical plane thereof issubstantially matched with the crystal plane {100}, a condition in whichthe traveling direction of the laser light transmitted through the planeparallel plate 32 is away from the crystal orientation <110> at somelevel, may be secured even when the plane parallel plate 32 is inclinedat the maximum level (e.g., about 32 degrees) with respect to theoptical axis AX. As a result, by substantially matching the optical axisof the plane parallel plate 32 with the crystal orientation <100>,changes in the polarization plane for the linearly polarized lighttransmitted through the plane parallel plate 32 may be avoidedregardless of the position of the plane parallel plate.

In the above descriptions, the traveling direction of the light isconfigured to come closer to the crystal orientation <111> or <100> thanto the crystal orientation <110> to avoid changes in the polarizationplane for the linearly polarized light transmitted through the lighttransmissive member positioned in the light path between the laser lightsource 1 and the polarized state switching device. However, theinvention is not limited to this. Similar configurations may beimplemented for the light transmissive member positioned in the lightpath between the polarized state switching device 42 and the mask M,which is an illuminated body (and therefore the wafer W), such that thechanges in the polarization plane for the linearly polarized light thatoriginate in fluorite may be avoided throughout the entire illuminationlight path.

Moreover, in the above descriptions, the traveling direction of thelight is configured to be closer to the crystal orientations <111> or<100> than to the crystal orientation <110> in order to avoid changes inthe polarization plane for the linearly polarized light transmittedthrough the light transmissive member formed by fluorite. However, theinvention is not limited to fluorite. Similar configuration may beimplemented for a light transmissive member formed by a cubic systemcrystal material, such as calcium fluoride, barium fluoride, andmagnesium fluoride, to avoid changes in the polarization plane for thelinearly polarized light originated in such a crystal material.

A plurality of rectangular prisms 33-38 (there are 6 in FIG. 9 as anexample) are provided for the beam matching unit BMU shown in FIG. 9. Ingeneral, even if the laser light source 1 is a KrF excimer laser lightsource or an ArF excimer laser light source, the linearly polarizedlight is changed to elliptically polarized light due to the totalreflection by the rectangular prisms that function as back surfacereflection mirrors when linearly polarized light enters the rectangularprisms, if the polarization plane for the incident linearly polarizedlight does not match the P-polarization plane or the S-polarizationplane (if the incident linearly polarized light is not P-polarized orS-polarized with respect to the reflection surface). The polarized stateswitching device 42 in the exemplary embodiment functions under theassumption that linearly polarized light is entering it, and thus maynot achieve the desired functions if elliptically polarized lightenters.

In the exemplary embodiment, as shown in FIG. 11, it may be preferableto additionally provide a quarter-wave plate 11 as a second phase memberfor converting the incident elliptically polarized light into linearlypolarized light, on the light source side (left side in FIG. 11) of thehalf-wave plate 10 in the polarized state switching device 42. Thequarter-wave plate 11 may be structured with its crystal optic axisbeing rotatable about the optical axis AX, for example. In this case, byconfiguring the crystal optic axis for the ¼ wavelength 11 in accordancewith the characteristics of the incident elliptically polarized light,the linearly polarized light enters the half-wave plate 10 to maintainthe proper functions of the polarized state switching device 42, even ifelliptically polarized light originating from the rectangular prism, forexample, enters the polarized state switching device 42. In FIG. 11, thequarter-wave plate 11 is positioned on the light source side of thehalf-wave plate 10. However, the quarter-wave plate 11 may be positionedon the mask side (right side in FIG. 11) of the half-wave plate.

In the above descriptions, a method for avoiding changes in thepolarization plane for linearly polarized light that is transmittedthrough the light transmissive members formed with fluorite, and amethod for maintaining the proper functioning of the polarized stateswitching device even if elliptically polarized light enters thepolarized state switching device as a result of the rectangular prisms,is applied in the embodiments shown in FIGS. 1-4. However, the inventionis not limited to these embodiments. These methods may be appliedsimilarly to the exemplary modifications of FIGS. 5-8.

Moreover, in the above descriptions, to avoid changes in thepolarization plane (changes in polarized state) for the linearlypolarized light that is transmitted through the light transmissivemembers formed with a cubic system crystal material, such as fluorite,the crystal orientation of such a crystal material is taken intoaccount. Instead of or in addition to this method, the lighttransmissive members formed by the cubic system crystal material may bekinematically held by using the method disclosed in U.S. PatentPublication U.S. 2002/0163741 A (or WO02/16993), each of which isincorporated herein by reference in its entirety. As a result, even ifthe light transmissive members expand due to heat generated when thelight having high energy density is transmitted through the lighttransmissive members formed with the cubic system crystal material, suchas fluorite, generation of applied double refraction that occurs in thelight transmissive members may be controlled, and changes in thepolarization plane (changes in the polarized state) for the linearlypolarized light that is transmitted though the light transmissivemembers may be controlled.

Next, improvement of image forming characteristics for the projectionoptical system (e.g., depth of focus and resolution) to perform well andaccurate transferring of the mask pattern by illuminating the mask withthe light having a predetermined polarized state for different types ofmask patterns is described in detail using examples. First, for dipoleillumination (generally, illumination that forms two separated areashaving a high light intensity distribution near or adjacent to the pupilplane), for example, the image forming characteristics of the projectionoptical system for a mask pattern 141 can be improved by forming twoplanar light sources 142 a and 142 b that are spaced away from eachother in the pitch direction (X direction: corresponding to the Xdirection on the mask) of a line-and-space pattern 141 formed on themask as shown in FIG. 14, and by illuminating the mask with light in thelinearly polarized state that has polarization planes (indicated bybi-directional arrows F1 in the figure) in a direction (Y direction:corresponding to the Z direction on the pupil plane) orthogonal to thedirection (X direction: corresponding to the X direction on the pupilplane) in which the two planar light sources 142 a and 142 b are spacedaway from each other. For a two-dimensional mask pattern, in whichpatterns in the vertical direction and patterns in the horizontaldirection are mixed, the pattern transfer may be performed at highthroughput by illuminating the mask with light in the nonpolarizedstate, without generating line width problems between the patterns inthe vertical direction and the patterns in the horizontal direction.

To sufficiently improve the image forming characteristics for theprojection optical system under the above-described dipole illumination,it is preferable to form the two planar light sources 142 a and 142 bsymmetrically about the optical axis AX and to satisfy the followingcondition (1):0.7≦σo  (1)

For the condition (1), σo is a value (normally called an outside σ)defined by φo/φp. As shown in FIG. 14, φo is a diameter of a circlecircumscribing the two planar light sources 142 a and 142 b about theoptical axis AX, and φp is a diameter of a pupil plane 143. To furtherimprove the image forming characteristics of the projection opticalsystem, it is preferable to set the lower value of the condition (1) at0.9.

Moreover, to sufficiently improve the image forming characteristics ofthe projection optical system under the above-described dipoleillumination, it is preferable to form the two planar light sources 142a and 142 b symmetrically about the optical axis AX and to satisfy thefollowing condition (2):0.5≦σi/σo  (2)

For the condition (2), σi is a value (normally called an inside σ)defined by φi/φp, and σo is the outside σ defined by φo/φp. As shown inFIG. 14, φi is a diameter of a circle inscribing the two planar lightsources 142 a and 142 b about the optical axis AX. To further improvethe image forming characteristics of the projection optical system, itis preferable to set the lower value of the condition (2) at 0.67 (≈⅔).

Next, for the circular illumination (generally, illumination that formsone area having a high light intensity distribution, having a centerthat is substantially on the optical axis on or adjacent to the pupilplane), for example, the image forming characteristics of the projectionoptical system with respect to the mask pattern 151 may be improved byusing a phase shift mask as the mask and by illuminating the mask withthe light in the linearly polarized state that has the polarizationplane in the direction (Y direction: corresponding to the Z direction onthe pupil plane) orthogonal to the pitch direction (X direction:corresponding to the X direction on the mask) of the line-and-spacepattern 151 formed on the phase shift mask, as shown in FIG. 15. Inaddition, in the circular illumination, similar to the case of thedipole illumination, the pattern may be transferred at high throughputby illuminating the mask with the light in the nonpolarized state, forexample.

In particular, to sufficiently improve the image forming characteristicsof the projection optical system in the above-described circularillumination, it is preferable to meet the following condition (3).σ≦0.4  (3)

In the condition (3), σ is a value (normally called a value σ) definedby φo/φp. As shown in FIG. 15, φ is a diameter of a circular planarlight source 152 (generally the size of the area with a high lightintensity distribution), and φp is a diameter of the pupil plane 153 asdescribed above. To further improve the image forming characteristics ofthe projection optical system, it is preferable to set the upper limitvalue for the condition (3) at 0.3.

Next, conditions that the light that is substantially in the linearlypolarized state or substantially in the nonpolarized state shouldsatisfy for this invention are described. First, it is preferable thatcomponent S1 of the Stokes parameter for the light that is substantiallyin the linearly polarized state herein, satisfies the followingcondition (4):0.6≦|S1|  (4)

In addition, it is preferable that components S1 and S2 of the Stokesparameter for the light that is substantially in the nonpolarized stateherein, satisfy the following conditions (5) and (6):|S1|≦0.1  (5)|S2|≦0.1  (6)

To make the light that is substantially in the linearly polarized statesufficiently closer to being linearly polarized, it is preferable to setthe lower limit value of the condition (4) at 0.8. For example, if anArF excimer laser that provides light with a wavelength of 193 nm isused as the light source, and if a numerical aperture for the projectionoptical system PL on the image side is 0.92, a depth of focus DOF (166nm) in the nonpolarized state may be improved to a depth of focus DOF(202 nm) for the vertical patterns, with an exposure amount error of 2%and a line width error of ±10% when φo and φi are set to 0.93 and 0.73,respectively, in the dipole illumination shown in FIG. 14 using a 6%halftone reticle (mask error: ±2 nm) having a line-and-space pattern at65 nm. If the condition (4), that is, the degree of polarization,exceeds 0.8, the change in line width due to changes in the degree ofpolarization may be substantially ignored. In the above-describedconditions, the generated line width difference is only 0.2 nm betweenthe degrees of polarization of 0.8 (|S1|=0.8) and 1.0(|S1|=1.0). Thisdifference may be substantially ignored. In other words, the values forthe condition (4) may fluctuate in the range of the degree ofpolarization between 0.8 and 1.0.

Moreover, to make the light substantially in the nonpolarized statecloser to the sufficiently nonpolarized light, it is preferable to setthe upper values for both of the conditions (5) and (6) at 0.04. If theconditions (5) and (6), that is, the degrees of polarization, are lowerthan 0.1, the line width difference due to the polarization may bereduced to less than 2 nm (the value σ is set at 0.2 (small σillumination) in the circular illumination shown in FIG. 15 using aphase shift mask having patterns isolated by 50 nm, with the lightsource wavelength of 193 nm and the image-side numerical aperture forthe projection optical system PL at 0.78). If the conditions (5) and(6), that is, the degrees of polarization, are lower than 0.4, the linewidth difference due to the polarization under the above-describedconditions may be reduced lower than 0.7 nm. Moreover, for theconditions (5) and (6), even if the degree of polarization is high whenmicroscopically viewing the area in the planar light source, the lightis considered to be substantially nonpolarized if the polarized statechanges with minute frequency within the area. Therefore, forcalculating the polarization degree distribution in the planar lightsource, a moving average may be used in an area of a size where thevalue σ becomes 0.1.

For the circular and annular illuminations, differences in the patternline width are generated between the vertical and horizontal directionsif a desired nonpolarized state, in which the degree of remainingpolarization is sufficiently low, is not achieved. In addition, for thedipole illumination, for example, improvement of the image formingcharacteristics for patterns with a narrow line width having apredetermined pitch direction may not be accomplished if the desiredlinearly polarized state that has the polarization plane in apredetermined direction is not achieved. Therefore, in the exemplarymodification of this embodiment, a polarization monitor is provided todetect the polarized state of the light that illuminates the mask M asthe illuminated surface (and therefore also the wafer W).

FIG. 16 is a diagram schematically showing a structure of the exposureapparatus shown in FIG. 1 that is additionally provided with apolarization monitor for detecting the polarized state of theillumination light. In the exposure apparatus according to an exemplarymodification shown in FIG. 16, the structure between the micro lensarray 8 and the mask M is different from that of the exposure apparatusshown in FIG. 1. That is, in this exemplary modification, the light beamfrom the secondary light source (generally, a predetermined lightintensity distribution formed on or adjacent to the pupil plane of theillumination optical system) formed on the rear focal plane of the microlens array illuminates superimposingly a mask blind MB after beingtransmitted through a beam splitter 51 and a condenser optical system 9a.

Accordingly, a rectangular illumination field corresponding to the shapeand focal length of each micro lens forming the micro lens array 8 isformed on the mask blind MB that functions as an illumination fielddiaphragm. Internal structures and functions of the polarization monitor50 that includes a beam splitter 51 will described later. The light beamtransmitted through the rectangular opening (light transmissive part) ofthe mask blind MB illuminates superimposingly the mask M, on which apredetermined pattern is formed, after being converged by the imageforming optical system 9 b. As a result, the image forming opticalsystem 9 b forms an image of the rectangular opening of the mask blindMB on the mask M.

Moreover, in the exposure apparatus according to the exemplarymodification shown in FIG. 16, the structures between the folding mirror3 and the diffractive optical element 4 are different from those in theexposure apparatus shown in FIG. 1. That is, in this exemplarymodification, the polarized state switching device (quarter-wave plate11, half-wave plate 10 and depolarizer 20) shown in FIG. 11 is providedinstead of the polarized state switching device (half-wave plate 10 andthe depolarizer 20) shown in FIG. 1. As described below, the output ofthe polarization monitor 50 is supplied to a control system 70. Inaddition, the control system 70 drives the polarized state switchingdevice (11, 10, 20) via a drive system 71. In the polarized stateswitching device having the structure shown in FIG. 11, an additionalquarter-wave plate may be used instead of the half-wave plate 10.

FIG. 17 is a perspective diagram schematically showing an internalstructure of the polarization monitor shown in FIG. 16. In FIG. 17, thepolarization monitor 50 is provided with the first beam splitter 51positioned in the light path between the micro lens array 8 and thecondenser optical system 9 a. The first beam splitter 51 has a form ofan uncoated plane parallel plate (i.e., bare glass) formed by a silicaglass and has a function to extract from the light path the reflectedlight having a polarized state different from the polarized state of theincident light.

The light extracted by the first beam splitter 51 from the light pathenters the second beam splitter 52. Similar to the first beam splitter51, the second beam splitter 52 has a form of an uncoated plane parallelplate formed by silica glass, for example, and has a function togenerate the reflected light in a polarized state different from thepolarized state of the incident light. The first beam splitter 51 andthe second beam splitter 52 are configured such that P-polarized lightfor the first beam splitter becomes S-polarized light for the secondbeam splitter, and S-polarized light for the first beam splitter 51becomes P-polarized light for the second beam splitter.

The light transmitted through the second beam splitter 52 is detected bythe first light intensity detector 53. The light reflected by the secondbeam splitter 52 is detected by the second light intensity detector 54.The outputs from the first light intensity detector 53 and the secondlight intensity detector 54 are both supplied to the control system 70.As discussed above, the control system 70 drives the quarter-wave plate11, the half-wave plate, and the depolarizer 20, which form thepolarized state switching device, via the drive system 71 as needed.

As described above, the reflectivity for P-polarized light and thereflectivity for S-polarized light are substantially different for thefirst beam splitter 51 and the second beam splitter 52. Therefore, inthe polarization monitor 50, the light reflected from the first beamsplitter 51 includes the S-polarized component of approximately 10% ofthe light incident to the first beam splitter 51 (S-polarization for thefirst beam splitter, which is the P-polarized component for the secondbeam splitter), for example, and the P-polarized component ofapproximately 1% of the light incident to the first beam splitter(P-polarization for the first beam splitter, which is the S-polarizedcomponent for the second beam splitter), for example.

Moreover, the light reflected from the second beam splitter 52 includesthe P-polarized component of approximately 0.1%, which is 1% of the 10%of the light incident to the first beam splitter 51 (P-polarization forthe first beam splitter, which is the S-polarized component for thesecond beam splitter), for example, and the S-polarized component ofapproximately 0.1%, which is 1% of the 10% of the light incident to thefirst beam splitter (S-polarization for the first beam splitter, whichis the P-polarized component for the second beam splitter), for example.

Accordingly, in the polarization monitor, the first beam splitter 51functions to extract from the light path the reflected light in apolarized state that is different from the polarized state of theincident light. As a result, although there is a slight effect bychanges in polarization due to the polarization characteristics of thesecond beam splitter, the polarized state (degree of polarization) ofthe light incident to the first beam splitter 51, and thus the polarizedstate of the light illuminating the mask M, may be detected based on theoutput of the first light intensity detector 53 (information related tothe strength of the light transmitted through the second beam splitter,that is, the information related to the intensity of the light in thepolarized state that is substantially the same as that for the lightreflected from the first beam splitter 51).

Furthermore, in the polarization monitor 50, the P-polarized light andthe S-polarized light for the first beam splitter are configured to beS-polarized light and P-polarized light for the second beam splitter,respectively. As a result, the amount (intensity) of the light incidentto the first beam splitter, and thus of the light illuminating the maskM, may be detected based on the output of the second light intensitydetector 54 (information related to the intensity of the lightsequentially reflected by the first beam splitter 51 and the second beamsplitter 52), without being substantially affected by the changes in thepolarized state for the light incident to the first beam splitter.

As such, using the polarization monitor 50, the polarized state of thelight incident to the first beam splitter 51 may be detected, and thus adetermination may be subsequently made as to whether the lightilluminating the mask M is in the desired nonpolarized state or linearlypolarized state. In addition, when the control system 70 confirms that,based on the detection result by the polarization monitor 50 that thelight illuminating the mask M (and subsequently the wafer W) has notbeen in the desired nonpolarized state or linearly polarized state, thequarter-wave plate 11, the half-wave plate 10 and the depolarizer 20,which form the polarized state switching device, are driven via thedrive system 71 for adjustment, so that the condition of the lightilluminating the mask M may be adjusted to the desired nonpolarizedstate or linearly polarized state.

As described above, the polarization monitor 50, the control system 70,the drive system 71, and the polarized state switching device (11, 10,20) which has a function to adjust the polarized state on theilluminated surface, are positioned in the light path between the lightsource 1 and the mask M and form a polarized state fluctuationcorrection device that corrects the fluctuation of the polarized stateon the mask M. In this case, it is preferable to avoid, as much aspossible, positioning optical members that have characteristics tochange and eject the polarized state of the incident light, such as anoptical member formed by a crystal optical material, such as fluoritethat has double refractivity (birefringence), or a quartz that hasoptical activity (rotary polarization, optical rotation), in the lightpath between the polarization monitor 50 and the mask M. Moreover, inthe light path between the polarization monitor 50 and the light source1 also, it is preferable to avoid, as much as possible, positioningoptical members that have characteristics to change the polarized stateof the light that is ejected. However, to secure the durability of theoptical member with respect to the illumination of light, it may benecessary to consider the effects from the changes in polarizationcaused by the optical members, such as the diffractive optical elements4 and 6, if such optical members are formed by fluorite or crystal.

Furthermore, in the above-descriptions, if the first light intensitydetector 53 is structured such that the light reflected from the firstbeam splitter 51 directly enters the first light intensity detector 53,the polarized state of the light incident to the first beam splitter 51may be detected highly accurately without having the output of the firstlight intensity detector 53 being affected by the polarizationfluctuation due to the polarization characteristics of the second beamsplitter 52. In addition, without being limited to the structure shownin FIG. 17, there are various exemplary modifications for the detailedstructure of the polarization monitor 50. Moreover, in the abovedescription, the polarized state switching device is structured by thequarter-wave plate 11, the half-wave plate 10 and the depolarizer 20.However, the polarized state switching device may be structured by thehalf-wave plate 10 and the depolarizer 20. In such a case, the controlsystem 70 drives the half-wave plate 10 and the depolarizer 20 via thedrive system 71 as needed.

In the above-descriptions, to highly accurately detect the polarizedstate of the light incident to the first beam splitter 51, it ispreferable that the first beam splitter 51 and the second beam splitter52 have reflective characteristics such that the reflectivity for theP-polarized light is sufficiently different from the reflectivity forthe S-polarized light. In detail, it is preferable that the first beamsplitter 51 and the second beam splitter 52 have reflectivecharacteristics such that the P-polarized light intensity Ip and theS-polarized light intensity Is, which are included in the lightreflected from the first beam splitter 51, satisfy a condition that anintensity ratio Ip/Is is less than ½ (Ip/Is<½) or more than 2 (Ip/Is>2).

In addition, in the above descriptions, beam splitters that have a formof a plane parallel plate are used to extract the reflected light fromthe light path. However, the invention is not limited to this. Thepolarized state of the light incident to the beam splitter may bedetected by using a beam splitter that extracts from the light path thelight transmitted in a polarized state different from the polarizedstate of the incident light and based on the intensity of thetransmitted light extracted from the light path by the beam splitter. Insuch a case, it is preferable that the beam splitter has transmissivecharacteristics such that the P-polarized light intensity Ip and theS-polarized light intensity Is, which are included in the lightreflected from the beam splitter, satisfy a condition that the intensityratio Ip/Is is less than ½ (Ip/Is<½) or more than 2 (Ip/Is>2).

As described above, it is possible that linearly polarized light fromthe laser light source 1 is changed to elliptically polarized light andenters the polarized state switching device (11, 10, 20) due to effectsof the total reflection by the rectangular prisms. In addition, it ispossible that linearly polarized light from the laser light source 1 ischanged to elliptically polarized light and enters the polarized stateswitching device (11, 10, 20) due to effects by an optical member, suchas one formed by fluorite, which has characteristics to change thepolarized state of the incident light.

In this case, in order to convert the elliptically polarized stateincident to the quarter-wave plate 11 into linearly polarized light, itscrystal optic axis should be set at a predetermined angular position inaccordance with the orientation of the long axis of the incidentelliptically polarized light. In addition, in order to convert thelinearly polarized light incident to the half-wave plate 10 intolinearly polarized light having a polarization plane in a predetermineddirection, the crystal optic axis should be set at a predeterminedangular position in accordance with the orientation of the polarizationplane of the incident linearly polarized light. A method of adjustingthe crystal optic axis for the quarter-wave plate and the crystal opticaxis for the half-wave plate is explained before with the polarizedstate switching device (11, 10, 20) shown in FIG. 11 as an example. Thebelow adjustment method may be generally applicable in any opticalsystem equipped with a half-wave plate and a quarter-wave plate, inwhich the crystal optic axes thereof are structured to be rotatableabout the optical axis.

FIG. 18 is a flow chart of a method for adjusting the crystal optic axesof the quarter-wave plate and of the half-wave plate in the polarizedstate switching device shown in FIG. 11. As described in FIG. 18, thedepolarizer 20 is removed from the light path, and the crystal opticaxes of the quarter-wave plate 11 and of the half-wave plate 10 areinitially set at the normal angular position, such as −45 degrees (S11).Next, while the crystal optic axis of the quarter-wave plate 11 is fixedat the normal angular position of −45 degrees, outputs are obtained fromthe polarization monitor 50 at each angular position of the crystaloptic axis of the half-wave plate 10 as the crystal optic axis of thehalf-wave plate 10 is rotated by +5 degrees, for example, from thenormal angular position of −45 degrees to an angular position of +45degrees (S12).

FIG. 19 is a graph showing the changes in the output of the polarizationmonitor at various angular positions of the crystal optic axis of thehalf-wave plate. In FIG. 19, the horizontal axis indicates the angularposition (degrees) of the crystal optic axis of the half-wave plate 10,and the vertical axis indicates the output (values for the Stokesparameter S1 component) of the polarization monitor 50. Next, as thecrystal optic axis of the quarter-wave plate 11 is rotated by +15degrees, for example, from the normal angular position of −45 degrees toan angular position of +45 degrees, outputs from the polarizationmonitor 50 are obtained at each angular position of the crystal opticaxis of the half-wave plate 10 for each angular position of the crystaloptic axis of the quarter-wave plate 10, as the crystal optic axis ofthe half-wave plate 10 is rotated by +5 degrees, for example, from thenormal angular position of −45 degrees to an angular position of +45degrees (S13).

FIG. 20 is a graph showing the changes in the output of the polarizationmonitor at various angular positions of the crystal optic axis of thehalf-wave plate for each angular position of the crystal optic axis ofthe quarter-wave plate. In FIG. 20, letter “a” indicates that thecrystal optic axis of the quarter-wave plate is at the normal angularposition of −45 degrees. Letter “b” indicates that the crystal opticaxis of the quarter-wave plate 11 is at the angular position of −30degrees. Letter “c” indicates that the crystal optic axis of thequarter-wave plate 11 is at the angular position of −15 degrees. Letter“d” indicates that the crystal optic axis of the quarter-wave plate 11is at the angular position of 0 degrees. Letter “e” indicates that thecrystal optic axis of the quarter-wave plate 11 is at the angularposition of +15 degrees. Letter “f” indicates that the crystal opticaxis of the quarter-wave plate 11 is at the angular position of +30degrees. Letter “g” indicates that the crystal optic axis of thequarter-wave plate is at the normal angular position of +45 degrees. Inaddition, similar to FIG. 19, the horizontal axis indicates the angularposition (degrees) of the crystal optic axis of the half-wave plate 10,and the vertical axis indicates the output of the polarization monitor50.

FIG. 21 is a graph showing the changes in output contrast of thepolarization monitor at various angular positions of the crystal opticaxis of the quarter-wave plate. In FIG. 21, the horizontal axisindicates the angular position (degrees) of the crystal optic axis ofthe quarter-wave plate 11, and the vertical axis indicates the outputcolor contrast (contrast of the changes in the Stokes parameter S1component) of the polarization monitor 50. The output contrast at eachangular position of the crystal optic axis of the quarter-wave plate 11,for example, is a value defined using the maximum and minimum values ofthe curves showing the output changes indicated by letters a-g in FIG.20 and by an equation contrast=(maximum value−minimum value)/(maximumvalue+minimum value).

The elliptically polarized light incident to the quarter-wave plate 11is converted to linearly polarized light when the crystal optic axis ofthe quarter-wave plate 11 is set such that the output contrast becomeslargest in FIG. 21. Therefore, in the adjustment method of thisembodiment, the angular position of the crystal optic axis of thequarter-wave plate 11, at which the output contrast becomes largest (theangular position of +30 degrees according to FIG. 21), is determined asthe desired first angular position for converting elliptically polarizedlight into linearly polarized light, by referring to the changes in theoutput contrast of the polarization monitor 50 at each angular positionof the crystal optic axis of the quarter-wave plate 11 (S14).

FIG. 22 is a graph showing the changes in the output of the polarizationmonitor at various angular positions of the crystal optic axis of thehalf-wave plate when the crystal optic axis of the quarter-wave plate isfixed at the first angular position, which is for convertingelliptically polarized light into linearly polarized light. In FIG. 22,the horizontal axis indicates the angular position (degrees) of thecrystal optic axis of the half-wave plate 10, and the vertical axisindicates the output of the polarization monitor 50. If the crystaloptic axis of the half-wave plate 10 is configured such that the outputof the polarization monitor 50 becomes the maximum or minimum in FIG.22, linearly polarized light incident to the half-wave plate 10 isconverted to linearly polarized light having V-polarization (verticalpolarization) or H-polarization (horizontal polarization).

In the adjustment method of this embodiment, by referring to the changesin the output of the polarization monitor 50 at various crystal opticaxes of the half-wave plate 10 when the crystal optic axis of thequarter-wave plate 11 is fixed at the first angular position, theangular position of the crystal optic axis of the half-wave plate 10 atthe time when the output of the polarization monitor becomes maximum orminimum (angular position of −17.5 or +27.5 degrees or adjacent theretoaccording to FIG. 22) is determined as the desired second angularposition for converting the incident linearly polarized light intolinearly polarized light having V- or H-polarization (S15).

Finally, the control system 70, via the drive system 71, adjusts theangular position of the crystal optic axis of the quarter-wave plate 11at the first angular position for converting the incident ellipticallypolarized light into linearly polarized light, and the angular positionof the crystal optic axis of the half-wave plate 10 at the secondangular position for converting the incident linearly polarized lightinto the linearly polarized light (e.g., V- or H-polarization) that hasa polarized plane in the predetermined direction (S16). Because theabove-described first and second angular positions may change inresponse to changes in illumination conditions (changes in the shape orsize of the light intensity distribution formed on the pupil plane ofthe illumination optical system or adjacent thereto), it is preferableto reset the crystal optic axes of the quarter-wave plate 11 and thehalf-wave plate 10 as needed. In the above embodiment, the quarter-waveplate and the half-wave plate are used for the polarized state switchingdevice. However, two quarter-wave plates may be used for the polarizedstate switching device.

The above explanations are based on an exposure apparatus equipped withan illumination optical system in which an illumination pupildistribution forming device for forming a predetermined light intensitydistribution on the pupil plane or adjacent thereto based on the lightbeam from a light source as shown in FIG. 1 or 16 includes twodiffractive optical elements (4, 6). However, this invention is notlimited to the structures shown in FIG. 1 or 16. There are variousmodifications for the structures of illumination optical systems towhich this invention may be applied. FIG. 23 is a diagram schematicallyshowing a structure of an exposure apparatus that has an illuminationpupil distribution forming device having a structure different from onesshown in FIG. 1 or 16.

The exposure apparatus according to the exemplary modification shown inFIG. 23 has a structure similar to that for the exposure apparatus shownin FIG. 16. However, the structures of the illumination pupildistribution forming device, that is, the structure between thediffractive optical element 4 and the micro lens array 8 is different.The structure and functions of the exemplary modification shown in FIG.23 are described below, focusing on the difference from the exposureapparatus shown in FIG. 16. In the exposure apparatus according to theexemplary modification shown in FIG. 23, the light beam that istransmitted through the diffractive optical element 4 a for annularillumination, for example, enters an afocal lens (relay optical system)85. The afocal lens 85 is an afocal system (afocal optical system)configured such that the position of a front focal point and theposition of the diffractive optical element 4 a substantially match eachother, and such that the position of a rear focal point and the positionof a predetermined plane 86 shown by dotted lines in the figuresubstantially match each other.

Therefore, a light beam with substantially parallel light rays thatenters the diffractive optical element 4 a exits from the afocal lens asa light beam with substantially parallel light rays after forming anannular light intensity distribution on the pupil plane of the afocallens 85. On the pupil or adjacent thereto in the light path between afront lens group 85 a and a rear lens group 85 b of the afocal lens 85,a conical axicon system 87, a first cylindrical lens pair 88, and asecond cylindrical lens pair 89 are positioned in order from the lightsource side. The detailed structure and functions thereof will bedescribed later. The basic structure and functions are described below,without reference to the functions of the conical axicon system 87, thefirst cylindrical lens pair 88, and the second cylindrical lens pair 89to simplify the explanations.

The light beam transmitted through the afocal lens 85 enters the microlens array 8, which functions as an optical integrator, through a zoomlens (variable power optical system) for varying the σ value. Thepredetermined plane 86 is positioned adjacent to the front side focalpoint of the zoom lens 90. The incident surface of the micro lens array8 is positioned adjacent to the rear focal point of the zoom lens 90. Inother words, the zoom lens 90 positions the predetermined plane 86 andthe incident surface of the micro lens array 8 in a substantial Fouriertransform relationship and thus positions the pupil plane of the afocallens 85 and the incident surface of the micro lens array 8 substantiallyin optical conjugation. Therefore, similar to the pupil plane of theafocal lens 85, on the incident surface of the micro lens array 8, anannular illumination field about the optical axis AX, for example, isformed. The total shape of the annular illumination field variessimilarly depending on the focal length of the zoom lens 90.

Each micro lens forming the micro lens array 8 has a rectangular crosssection similar to the shape of the illumination field to be formed onthe mask M (and thus the shape of the exposure region to be formed onthe wafer W). The light beam that enters the micro lens array 8 istwo-dimensionally divided by the large number of micro lenses. On therear focal plane (and thus the illumination pupil) is formed a secondarylight source having a light intensity that is substantially the same asthe illumination field formed by the light beam incident to the microlens array 8, that is, a secondary light source formed by a substantialplanar light source in an annular shape about the optical axis AX.

FIG. 24 is a diagram schematically showing the structure of the conicalaxicon system provided in the light path between the front and rear lensgroups of the afocal lens shown in FIG. 23. The conical axicon system 87is structured from, in order from the light source side, the first prismmember 87 a, having a flat surface that faces to the light source sideand a concave conical refractive surface that faces to the mask side,and the second prism member 87 b, having a flat surface that faces tothe mask side and a convex conical refractive surface that faces to thelight source side.

The concave conical refractive surface of the first prism member 87 aand the convex conical refractive surface of the second prism member 87b are formed complementarily so as to be contactable to each other. Inaddition, at least one of the first prism member 87 a and the secondprism member 87 b is structured so as to be movable along the opticalaxis AX so that the space between the concave conical refractive surfaceof the first prism member 87 a and the convex conical refractive surfaceof the second prism member 87 b is variable.

When the concave conical refractive surface of the first prism member 87a and the convex conical refractive surface of the second prism member87 b are in contact with each other, the conical axicon system 87functions as a plane parallel plate. Therefore, the annular secondarylight source formed is not affected. However, when the concave conicalrefractive surface of the first prism member 87 a and the convex conicalrefractive surface of the second prism member 87 b are separated, theconical axicon system 87 functions as a so-called beam expander.Therefore, the angle of the light beam incident to the predeterminedplane 86 varies in accordance with the changes of the space in theconical axicon system 87.

FIG. 25 is a diagram that explains functions of the conical axiconsystem with respect to the secondary light source formed in annularillumination in the exemplary modification shown in FIG. 23. In theannular illumination in the exemplary modification shown in FIG. 23, byincreasing the space in the conical axicon system 87 from zero to apredetermined value, the smallest annular secondary light source 130 a,which is formed when the space in the conical axicon system 87 is zeroand when the focal length of the zoom lens 90 is set at the smallestvalue (hereinafter referred as “normal state”), is changed to an annularsecondary light source 130 b, of which both outer and inner diametersare expanded, without changing the width (½ of the difference betweenthe outer and inner diameters as indicated by arrows). In other words,the annular ratio (inner diameter/outer diameter) and the size (outerdiameter) are both changed by the operation of the conical axicon system87 without changing the width of the annular secondary light source.

FIG. 26 is a diagram explaining the function of the zoom lens withrespect to the secondary light source formed in the annular illuminationin the exemplary modification shown in FIG. 23. In the annularillumination in the exemplary modification shown in FIG. 23, the annularsecondary light source 130 a formed in the normal state is changed to anannular secondary light source 130 c, having a total shape that isexpanded similarly by expanding the focal length of the zoom lens 90from the smallest value to a predetermined value. In other words, boththe width and the size (outer diameter) of the annular secondary lightsource are changed by the operation of the zoom lens 90 without changingthe annular ratio.

FIG. 27 is a diagram schematically showing a structure of the first andsecond cylindrical lens pairs provided in the light path between thefront and rear lens groups of the afocal lens shown in FIG. 23. In FIG.27, the first cylindrical lens pair 88 and the second cylindrical lenspair 89 are provided in order from the light source side. The firstcylindrical lens pair 88 is structured by, from the light source side,the first cylindrical negative lens 88 a having negative refractivepower in the YZ plane and no refractive power in the XY plane, and thefirst cylindrical positive lens 88 b having positive refractive power inthe YZ plane and no refractive power in the XY plane, for example.

On the other hand, the second cylindrical lens pair 89 is structured by,from the light source side, the second cylindrical negative lens 89 ahaving negative refractive power in the XY plane and no refractive powerin the YZ plane, and the second cylindrical positive lens 89 b havingthe positive refractive power in the XY plane and no refractive power inthe YZ plane, for example. The first cylindrical negative lens 88 a andthe first cylindrical positive lens 88 b are structured so as to beintegrally rotatable about the optical axis AX. Similarly, the secondcylindrical negative lens 89 a and the second cylindrical positive lens89 b are structured so as to be integrally rotatable about the opticalaxis AX.

Accordingly, in a state shown in FIG. 27, the first cylindrical lenspair 88 functions as a beam expander having power in the Z direction,and the second cylindrical lens pair 89 functions as a beam expanderhaving power in the X direction. In the exemplary modification shown inFIG. 23, the power for the first cylindrical lens pair 88 and the powerfor the second cylindrical lens pair 89 are set to be the same.

FIGS. 28-30 are diagrams explaining the operation of the first andsecond cylindrical lens pairs with respect to the secondary light sourceformed in the annular illumination in the exemplary modification shownin FIG. 23. In FIG. 28, the direction of the power of the firstcylindrical lens pair 88 is set to form an angle of +45 degrees from theZ axis about the optical axis AX, and the direction of the power of thesecond cylindrical lens pair 89 is set to form an angle of −45 degreesfrom the Z axis about the optical axis AX.

Therefore, the directions of the power of the first cylindrical lenspair 88 and the second cylindrical lens pair 89 intersect at rightangles to each other, and the power in the Z direction and the power inthe X direction become the same in a combined system of the firstcylindrical lens pair 88 and the second cylindrical lens pair 89. As aresult, in a perfect circle state shown in FIG. 28, the light beam thatis transmitted through the combined system of the first cylindrical lenspair 88 and the second cylindrical lens pair 89 is expanded with thesame power in the Z and X directions. Therefore, a perfect annularsecondary light source is formed on the illumination pupil.

In FIG. 29, the direction of the power of the first cylindrical lenspair 88 is set to form an angle of +80 degrees, for example, withrespect to the Z direction about the optical axis AX, and the directionof the power of the second cylindrical lens pair 89 is set to form anangle of −80 degrees, for example, with respect to the Z direction aboutthe optical axis AX. Therefore, the power in the X direction becomeslarger than the power in the Z direction in the combined system of thefirst cylindrical lens pair 88 and the second cylindrical lens pair 89.As a result, in a horizontally elliptical state shown in FIG. 29, thelight beam that is transmitted through the combined system of the firstcylindrical lens pair 88 and the second cylindrical lens pair 89 isexpanded with larger power in the X direction than in the Z direction.Therefore, a horizontally long annular secondary light source that iselongated in the X direction is formed on the illumination pupil.

In FIG. 30, the direction of the power of the first cylindrical lenspair 88 is set to form an angle of +10 degrees, for example, withrespect to the Z direction about the optical axis AX, and the directionof the power of the second cylindrical lens pair 89 is set to form anangle of −10 degrees, for example, with respect to the Z direction aboutthe optical axis AX. Therefore, the power in the Z direction becomeslarger than the power in the X direction in the combined system of thefirst cylindrical lens pair 88 and the second cylindrical lens pair 89.As a result, in a vertically elliptical state shown in FIG. 30, thelight beam that is transmitted through the combined system of the firstcylindrical lens pair 88 and the second cylindrical lens pair 89 isexpanded with larger power in the Z direction than in the X direction.Therefore, a vertically long annular secondary light source that iselongated in the Z direction is formed on the illumination pupil.

Further, by setting first cylindrical lens pair 88 and the secondcylindrical lens pair 89 in any state between the perfect circular stateshown in FIG. 28 and the horizontally elliptical state shown in FIG. 29,horizontally annular secondary light sources in accordance with variousvertical/horizontal ratios can be formed. In addition, by setting firstcylindrical lens pair 88 and the second cylindrical lens pair 89 in anystate between the perfect circular state shown in FIG. 28 and thevertically elliptical state shown in FIG. 30, vertically annularsecondary light sources in accordance with various vertical/horizontalratios can be formed. In the exemplary modification shown in FIG. 23,circular illumination and various modified illuminations may be achievedby setting a diffractive optical element for the circular illuminationor a diffractive optical element for multi-pole (e.g., quadrupole)illumination, instead of the diffractive optical element 4 a for annularillumination. Therefore, in the exemplary modifications shown in FIGS.23-30, the polarized state for the illumination light can be changed inaccordance with the pattern characteristics of the mask M, and thevertical/horizontal ratio of the secondary light source formed on theillumination pupil may be adjusted as needed. As such, excellentexposure may be performed with an appropriate illumination conditionachieved in accordance with the pattern characteristics of the mask M.

In addition, in each of the above-described embodiments and exemplarymodifications, if there are fluctuations in uneven illumination on theilluminated surface, fluctuations in the light intensity distribution onthe pupil plane, and/or fluctuations in telecentricity on theilluminated surface when switching between the linearly polarized stateand the nonpolarized state or between the X-polarized state and theY-polarized state, it is preferable to reduce the fluctuations in theuneven illumination, the fluctuations in the light intensitydistribution on the pupil plane, and/or the fluctuations in thetelecentricity by controlling the uneven illumination, the lightintensity distribution on the pupil plane and/or the telecentricity inaccordance with the changes in the polarized state on the illuminatedsurface.

For example, the uneven illumination on the illuminated surface can becontrolled by changing the lens position and orientation of at least apart of the plurality of lens elements forming the condenser opticalsystem 9 shown in FIG. 1 or the condenser optical system 9 a shown inFIG. 16 or 23. In addition, in the light path between the condenseroptical system 9 and the mask M shown in FIG. 1 or in the light pathbetween the condenser optical system 9 and the mask blind MB shown inFIG. 16 or 23, a density filter plate disclosed in Japanese Laid-OpenPatent Application No. 2002-100561 (and corresponding U.S. PatentPublication No. 2003/0025890A, which is incorporated herein by referencein its entirety) or disclosed in Japanese Laid-Open Patent ApplicationNo. 2003-92253 (and corresponding U.S. Patent Publication No.2003/0067591A. which is incorporated herein by reference in itsentirety) may be positioned. By controlling rotational angle andposition of the density filter plate, the uneven illumination on theilluminated surface can be controlled. Moreover, instead of or in theproximity of the mask blind MB shown in FIG. 16 or 23, a variable bladedisclosed by Japanese Laid-Open Patent Application No. 2002-184676, forexample, may be provided. The uneven illumination on the illuminatedsurface can also be controlled by setting the variable blade such thatthe width of the exposure region in the scanning direction may bedifferent from that in the non-scanning direction.

Furthermore, the light intensity distribution on the pupil plane can becontrolled by positioning the density filter plate disclosed in theabove Japanese Laid-Open Patent Application No. 2002-100561 (U.S. PatentPublication No. 2003/0025890A) and Japanese Laid-Open Patent ApplicationNo. 2003-92253 (U.S. Patent Publication No. 2003/0067591A) adjacent tothe illumination pupil, such as adjacent to the exit side of the microlens array 8.

The telecentricity can be controlled by changing the lens position andorientation of at least a part of the plurality of lens elements formingthe condenser optical system 9 shown in FIG. 1 or the condenser opticalsystem 9 a shown in FIG. 16 or 23.

In addition, by pre-calculating the relationships between theconfiguration of the polarized state switching device (insertion/removalof the depolarizer, a rotational angle of the half-wave plate, and arotational angle of the quarter-wave plate) and the condition of theuneven illumination on the illuminated surface, the light intensitydistribution on the pupil plane and the telecentricity, the unevenillumination on the illuminated surface, the light intensitydistribution on the pupil plane and the telecentricity can be controlledin accordance with the configuration of the polarized state switchingdevice. Furthermore, by measuring the uneven illumination on theilluminated surface, the light intensity distribution on the pupilplane, and the telecentricity on the illuminated surface or a surfaceoptically conjugate to the illuminated surface, the uneven illuminationon the illuminated surface, the light intensity distribution on thepupil plane, and the telecentricity may also be controlled in accordancewith the result of the measurement.

In the above-described embodiments and exemplary modifications, themicro lens array 8, which is formed by a plurality of micro lenseshaving positive refractive power densely arranged in a matrix, is usedas an optical integrator. However, instead of the micro lens array 8, acylindrical micro lens array, which has a first one-dimensionalcylindrical lens array arranged in a pitch along a predetermined firstdirection and a second one-dimensional cylindrical lens array arrangedin a pitch along a second direction orthogonal to the first direction,may be used. It is preferable that the first and second one-dimensionalcylindrical lens arrays of the cylindrical micro lens array are providedintegrally with a single light transmissive substrate, and moreparticularly preferable that a plurality of cylindrical lens arrayplates having the first and second one-dimensional cylindrical lensarrays are provided and positioned spaced from each other along thedirection of the optical axis. In addition, it is preferable that atleast one of the pitch of the first one-dimensional cylindrical lensarray in the first direction and the pitch of the second one-dimensionallens array in the second direction is less than 2 mm.

With this structure, unlike the ordinary fly's-eye lens, for which eachrefractive surface is formed in two-dimensional curvature (sphericalshape), each refractive surface of the first and second one-dimensionalcylindrical lens arrays of the cylindrical micro lens array is formed inone-dimensional curvature (cylindrical shape). Therefore, highlyprecision processes become easy, and thus, the manufacturing cost may bedecreased. In particular, for the cylindrical micro lens array, in whichthe smallest pitch is 2 mm or less, the reduction in the manufacturingcost is significant. In addition, such a cylindrical micro lens arraycan be manufactured by grinding, etching, and/or tool-pressingprocesses.

By use of a cylindrical micro lens array that is highly precise in shapeand manufactured at low cost, illumination with excellent uniformity maybe achieved. Therefore, in combination with an enormous improvement inimage forming characteristics using polarized illumination, micropatterns may be formed with high transfer accuracy throughout the entireexposure regions.

A cylindrical micro lens array is proposed in the specification anddrawings of Applicant's Japanese Patent Application No. 2002-152634 (andcorresponding U.S. Patent Publication No. 2004/0036977A). The presentspecification incorporates by reference the disclosure of U.S. PatentPublication No. 2004/0036977A in its entirety.

In the exposure apparatus according to the above-described embodiments,micro devices (semiconductor elements, imaging elements, liquid crystaldisplay elements, thin film magnetic heads, etc.) may be manufactured byilluminating a mask (reticle) by an illumination optical system andexposing a transfer pattern formed on the mask onto a photosensitivesubstrate using a projection optical system. An exemplary method forobtaining a semiconductor device, as the micro device, by forming apredetermined circuit pattern on a wafer or the like, as thephotosensitive substrate, using the exposure apparatus according to theabove-described embodiments is explained below with reference to a flowchart shown in FIG. 12.

First, in step 301 in FIG. 12, a metallic film is vapor-deposited on thewafers of one lot. In next step 302, photoresist is applied onto themetallic film on the wafers of one lot. Thereafter, in step 303, usingthe exposure apparatus of the above-described embodiments, an image of apattern on a mask is sequentially exposed and transferred onto each shotregion on the wafers of one lot through a projection optical system.Then, after the photoresist on the wafers of one lot is developed instep 304, by etching the resist pattern on the wafers of one lot as amask, a circuit pattern corresponding to the pattern on the mask isformed in each shot region on each wafer in step 305. By forming acircuit pattern on an upper layer, for example, a device such as asemiconductor device can be manufactured. According to theabove-described method for manufacturing semiconductor devices, thesemiconductor devices having an extremely micro circuit pattern may beobtained at good throughput.

Furthermore, in the exposure apparatus of the above-describedembodiments, liquid crystal display elements may be obtained as themicro device by forming a predetermined pattern (circuit pattern,electrode pattern, etc.) on a plate (glass substrate). An exemplarymethod is explained below with reference to a flow chart shown in FIG.13. In FIG. 13, in a pattern formation step 401, a so-calledphotolithography process is performed, in which a mask pattern istransferred and exposed onto a photosensitive substrate (a glasssubstrate or the like applied with resist) using the exposure apparatusin the above-described embodiments. By this photolithography process, apredetermined pattern that may include a large number of electrodes orthe like is formed on the photosensitive substrate. Thereafter, thepredetermined pattern is formed on the substrate as the exposedsubstrate proceeds with developing, etching, and resist removalprocesses. Then, the color filter formation step 402 is performed.

Next, in the color filter formation step 402, a color filter is formed,in which a large number of groups of three dots corresponding to R(red), G (green) and B (blue) is arranged in a matrix, or in which aplurality of groups of three strip filters corresponding to R, G and B,is arranged in the horizontal scan line direction. Then, after the colorfilter formation step 402, a cell assembly step 403 is performed. In thecell assembly step 403, a liquid crystal panel (liquid crystal cell) isassembled using the substrate having the predetermined pattern that isobtained in the pattern formation step 401 and the color filter obtainedin the color filter formation step 402.

In the cell assembly step 403, the liquid crystal panel (liquid crystalcell) is manufactured by, for example, injecting liquid crystal materialbetween the substrate having the predetermined pattern that is obtainedin the pattern formation step 401 and the color filter obtained in thecolor filter formation step 402. Then, in a module assembly step 404,various parts, such as an electric circuitry and a backlight, thatperform display operation for the assembled liquid crystal panel (liquidcrystal cell) and provided to complete the process. According to theabove-described method for manufacturing liquid crystal displayelements, liquid crystal display elements having extremely micro circuitpatterns can be obtained with good throughput.

In the embodiment shown in FIG. 1, the mask is illuminatedsuperimposingly by collecting the light from the secondary light sourceby the condenser optical system 9. However, this invention is notlimited to this. As shown in the exemplary modification shown in FIG.16, an illumination field diaphragm (mask blind) and a relay opticalsystem that forms an image of the illumination field diaphragm on themask M may be arranged in the light path between the condenser opticalsystem 9 and the mask M. In this case, the condenser optical system 9illuminates the illumination field diaphragm superimposingly bycollecting the light from the secondary light source. Therefore, therelay optical system forms on the mask M an image of an opening (lighttransmissive part) of the illumination field diaphragm.

Furthermore, in the above-described embodiments, KrF excimer laser light(wavelength: 248 nm) or ArF excimer laser light (wavelength: 193 nm) isused as the exposure light. However, the invention is not limited tothis. This invention may be applied to other appropriate laser lightsources, such as an F₂ laser light source that provides laser light at awavelength of 157 μm, and light sources other than laser light sources,such as a lamp light source that provides ultraviolet light, such asi-line, g-line and h-line. Moreover, in the above-described embodiments,this invention is explained with respect to a projection exposureapparatus equipped with an illumination optical system as an example.However, this invention may be applied to a general illumination opticalsystem for illuminating an illuminated surface other than a mask.

In addition, in the above-described embodiment, a so-called immersionmethod is used, in which the light path between the projection opticalsystem and the photosensitive substrate is filled with a medium(typically liquid) having a refractivity greater than 1.1. In this case,as the method that fills the light path between the projection opticalsystem and the photosensitive substrate with liquid, a method disclosedin International Publication No. WO99/49504 that locally fills withliquid, a method disclosed in Japanese Laid-Open Patent Application No.6-124873 that moves a stage holding a substrate that is the object ofexposure in a liquid tank, and a method disclosed in Japanese Laid-OpenPatent Application No. 10-303114 that forms a liquid tank having apredetermined depth on a stage and holds a substrate therein, may beused. The disclosure of WO99/49504 is incorporated herein by referencein its entirety.

As the liquid, it is preferable to use one that has transmissivity forthe exposure light, has a high refractivity, and is stable for aphotoresist applied on the projection optical system and/or substrate.For example, purified water and deionized water may be used when KrFexcimer laser light or ArF excimer laser light is used as the exposurelight. Moreover, fluorinated liquid, such as fluorinated oil orfluoropolyether (PFPE), which can transmit F₂ laser light, may be usedas the liquid when the F₂ laser light is used as the exposure light.

Furthermore, this invention may be used in a twin-stage type exposureapparatus disclosed in Japanese Laid-Open Patent Application Nos.10-163099 and 10-214783 (and corresponding U.S. Pat. No. 6,400,441, thedisclosure of which is incorporated herein by reference in itsentirety), and PCT Publication No. 2000-505958 (and corresponding U.S.Pat. No. 5,969,441, the disclosure of which is incorporated herein byreference in its entirety), which provides two stages that holdprocessed substrates, such as wafers, separately and are independentlymovable in the XY directions.

As described above, in the illumination optical system of thisinvention, the polarized state of the light that illuminates theilluminated surface may be switched between a specified polarized state(e.g., linearly polarized state) and nonpolarized state by the functionof the polarized state switching device structured from a half-waveplate and a depolarizer (nonpolarized element). Therefore, when theillumination optical system of this invention is installed an exposureapparatus, for example, excellent illumination conditions can beachieved by changing the polarized state of the illumination light whilecontrolling the loss of light amount in accordance with thecharacteristics of mask patterns.

Moreover, in the exposure apparatus that uses the illumination opticalsystem and exposure method of this invention, because excellentillumination conditions may be achieved by changing the polarized stateof the illumination light in accordance with the characteristics of thepattern on the mask M, excellent exposure can be performed under theexcellent illumination conditions achieved in accordance with thecharacteristics of the patterns on the mask M. Therefore, excellentdevices at a high throughput can be manufactured.

While the invention has been described with reference to preferredembodiments thereof, it is to be understood that the invention is notlimited to the preferred embodiments or constructions. The invention isintended to cover various modifications and equivalent arrangements. Inaddition, while the various elements of the preferred embodiments areshown in various combinations and configurations, that are exemplary,other combinations and configurations, including more, less or only asingle element, are also within the spirit and scope of the invention.

1. An illumination optical system that illuminates an illuminatedsurface with light from a light source that provides linearly polarizedlight, comprising: a polarized state switching device positioned in alight path between the light source and the illuminated surface, thepolarized state switching device switches a polarized state of the lightthat illuminates the illuminated surface between a predeterminedlinearly polarized state and a nonpolarized state while controlling aloss of light amount, and varies a polarization plane of thepredetermined linearly polarized light.
 2. The illumination opticalsystem of claim 1, wherein the polarized state switching device includesa phase member for selectively changing a polarization plane of theincident linearly polarized light.
 3. The illumination optical system ofclaim 2, wherein the phase member includes a half-wave plate including acrystal optic axis that is rotatable about an optical axis of theillumination optical system.
 4. The illumination optical system of claim2, wherein the polarized state switching device further includes asecond phase member for converting incident elliptically polarized lightinto linearly polarized light.
 5. The illumination optical system ofclaim 4, wherein the second phase member includes a quarter-wave plateincluding a crystal optic axis that is rotatable about an optical axisof the illumination optical system.
 6. The illumination optical systemof claim 1, wherein a light transmissive member is positioned in thelight path between the light source and the polarized state switchingdevice and is formed by a cubic system crystal material, the lighttransmissive member being configured such that a traveling direction ofthe light becomes closer to a crystal orientation <111> or <100> than acrystal orientation <110>.
 7. The illumination optical system of claim6, wherein the light transmissive member includes an optical memberfixedly positioned in the light path, and an optical axis of the opticalmember is configured to substantially match the crystal orientation<111> or <100>.
 8. The illumination optical system of claim 6, whereinthe light transmissive member includes a rectangular prism as a rearsurface reflection mirror, an incident surface and an exit surface ofthe rectangular prism are configured to substantially match a crystalplane {100}, and a reflection surface of the rectangular prism isconfigured to substantially match a crystal plane {110}.
 9. Theillumination optical system of claim 6, wherein the light transmissivemember includes a plane parallel plate for moving light entering alongthe optical axis in parallel, the light transmissive member beingprovided in the light path and inclinable with respect to the opticalaxis, and the optical axis of the plane parallel plate substantiallymatches the crystal orientation <100>.
 10. The illumination opticalsystem of claim 1, wherein an S1 component of a Stokes parameter of thelight satisfies the below condition in the predetermined polarizedstate:0.6≦|S1|.
 11. The illumination optical system of claim 1, furthercomprising a polarized state fluctuation correcting device that correctsfluctuations of the polarized state on the illuminated surface, thepolarized state fluctuation correcting device being positioned in thelight path between the light source and the illuminated surface.
 12. Theillumination optical system of claim 11, wherein the polarized statefluctuation correcting device comprises a polarization monitorpositioned in the light path between the polarized state switchingdevice and the illuminated surface to detect the polarized state of thelight, and a controller that controls the polarized state switchingdevice in response to an output from the polarization monitor.
 13. Theillumination optical system of claim 12, wherein the polarized stateswitching device comprises a half-wave plate including a crystal opticaxis that is rotatable about the optical axis of the illuminationoptical system, and a quarter-wave plate including a crystal optic axisthat is rotatable about the optical axis of the illumination opticalsystem, and in response to changes in detection results obtained fromthe polarization monitor when respectively changing the crystal opticaxes of the quarter-wave plate and the half-wave plate, the controlleradjusts an angular position of the crystal optic axis of thequarter-wave plate to a predetermined position for converting incidentelliptically polarized light into linearly polarized light and anangular position of the crystal optic axis of the half-wave plate to apredetermined position for converting incident linearly polarized lightinto linearly polarized light that includes a polarization plane in apredetermined direction.
 14. The illumination optical system of claim13, wherein the controller adjusts the angular position of the crystaloptic axis of the quarter-wave plate to a first angular position, atwhich a contrast for changes in an S1 component of the Stokes parameterin the detection result becomes substantially maximum when the crystaloptic axis of the quarter-wave plate is changed, and the angularposition of the crystal optic axis of the half-wave plate to a secondangular position, at which the S1 component of the Stokes parameter inthe detection result becomes substantially maximum or substantiallyminimum when the crystal optic axis of the half-wave plate is changedwhile the crystal optic axis of the quarter-wave plate is set at thefirst angular position.
 15. The illumination optical system of claim 12,wherein the polarization monitor is positioned in the light path betweenthe polarized state switching device and the illuminated surface andincludes a beam splitter that extracts from the light path reflectedlight or transmitted light in a polarized state different from thepolarized state of the incident light, and a light intensity detectorthat detects an intensity of the reflected light or the transmittedlight extracted by the beam splitter, and the polarized state of theincident light to the beam splitter is detected based on an output ofthe light intensity detector.
 16. The illumination optical system ofclaim 15, wherein the beam splitter includes reflectivity ortransmissivity, in which an intensity Ip for P-polarized light and anintensity Is for S-polarized light included in the reflected light orthe transmitted light satisfy a condition that an intensity ratio Ip/Isis less than ½ (Ip/Is <½) or more than 2 (Ip/Is >2).
 17. Theillumination optical system of claim 1, further comprising anillumination pupil distribution forming device that forms apredetermined light intensity distribution on or adjacent to a pupilplane of the illumination optical system, wherein the illumination pupildistribution forming device forms two areas including a high lightintensity distribution that are spaced along a direction of the pupilplane or a surface adjacent thereto that corresponds to a predeterminedfirst direction on the illuminated surface, and the polarized stateswitching device sets the polarized state of the light that illuminatesthe illuminated surface from the two areas including a high lightintensity distribution to the linearly polarized state that includes apolarization plane in a direction substantially orthogonal to thepredetermined first direction.
 18. The illumination optical system ofclaim 17, wherein the two areas including a high light intensitydistribution are formed symmetrically about the optical axis of theillumination optical system, and a value σo defined by a ratio φo/φpsatisfies the following condition: 0.7≦σo where φo is a diameter of acircle about the optical axis that circumscribes the two areas includinga high light intensity distribution, and φp is a diameter of the pupilplane.
 19. The illumination optical system of claim 17, wherein the twoareas including a high light intensity distribution are formedsymmetrically about the optical axis of the illumination optical system,and a value σo defined by a ratio φo/φp and σi defined by a ratio φi/φpsatisfy the following condition: 0.5≦σi/σo where φo is a diameter of acircle about the optical axis that circumscribes the two areas includinga high light intensity distribution, φp is a diameter of the pupilplane, and φi is a diameter of a circle about the optical axis thatinscribes the two areas including a high light intensity distribution.20. An exposure apparatus, comprising the illumination optical system ofclaim
 1. 21. The exposure apparatus of claim 20, further comprising: aprojection optical system positioned in the light path between a firstplane at which the mask is positioned, and a second plane at which thephotosensitive substrate is positioned, the projection optical systemforming an image of a pattern on the mask onto the second plane; a pupilintensity distribution forming device that forms a predetermined lightintensity distribution at a position conjugate to a pupil of theprojection optical system or a position adjacent thereto; and a pupilintensity distribution changing device that changes at least one of ashape and a size of the predetermined light intensity distribution. 22.The exposure apparatus of claim 21, further comprising a polarized statechanging device that is positioned in the light path between the lightsource and the illuminated surface and changes the polarized state ofthe light that illuminates the illuminated surface, wherein the pupilintensity distribution changing device changes at least one of the shapeand the size of the predetermined light intensity distribution inaccordance with pattern characteristics of the mask, and the polarizedstate changing device changes the polarized state of the light thatilluminates the illuminated surface in accordance with at least one ofthe shape and the size of the predetermined light intensitydistribution.
 23. The exposure apparatus of claim 22, wherein thepolarized state changing device comprises the polarized state switchingdevice that switches the polarized state of the light that illuminatesthe illuminated surface between a predetermined polarized state and anonpolarized state, and the polarized state switching device switchesbetween the predetermined polarized state and the nonpolarized state inaccordance with a change in at least one of the shape and the size ofthe predetermined light intensity distribution.
 24. The exposureapparatus of claim 22, wherein the pupil intensity distribution formingdevice forms two areas including a high light intensity distributionthat are spaced away from each other along a pitch direction of aline-and-space pattern formed on the mask, and the polarized statechanging device sets the polarized state of the light that illuminatesthe illuminated surface from the two areas including a high lightintensity distribution to a linearly polarized state that includes apolarization plane in a direction orthogonal to the pitch direction. 25.The exposure apparatus of claim 24, wherein the two areas including ahigh light intensity distribution are formed symmetrically about theoptical axis of the illumination optical system, and a value σo definedby a ratio φo/φp satisfies the following condition: 0.7≦σo where φo is adiameter of a circle about the optical axis that circumscribes the twoareas including a high light intensity distribution, and φp is adiameter of the pupil plane.
 26. The exposure apparatus of claim 24,wherein the two areas including a high light intensity distribution areformed symmetrically about the optical axis of the illumination opticalsystem, and a value σo defined by a ratio φo/φp and σo defined by aratio φi/φp satisfy the following condition: 0.5≦σo/σi where φo is adiameter of a circle about the optical axis that circumscribes the twoareas including a high light intensity distribution, φp is a diameter ofthe pupil plane, and φi is a diameter of a circle about the optical axisthat inscribes the two areas including a high light intensitydistribution.
 27. The exposure apparatus of claim 22, wherein the pupilintensity distribution forming device forms one area including a highlight intensity distribution substantially about the optical axis of theillumination optical system, and the polarized state changing devicesets the polarized state of the light that illuminates the illuminatedsurface from the one area including a high light intensity distributionto the linearly polarized state that includes a polarization plane in adirection substantially orthogonal to the pitch direction of theline-and-space pattern formed on a phase shift mask as the mask.
 28. Theexposure apparatus of claim 27, wherein a value σthat is defined by aratio φo/φp satisfies the following condition: σ≦0.4 where φo is a sizeof the one area including a high light intensity distribution, and φp isa diameter of the pupil plane.
 29. An illumination optical system thatilluminates an illuminated surface with light from a light source thatprovides linearly polarized light, comprising: a polarized stateswitching device positioned in a light path between the light source andthe illuminated surface, the polarized state switching device switches apolarized state of the light that illuminates the illuminated surfacebetween a predetermined linearly polarized state and a nonpolarizedstate while controlling a loss of light amount, wherein the polarizedstate switching device comprises a depolarizer that unpolarizes theincident linearly polarized light, the depolarizer being insertable intoand removable from an illumination light path.
 30. The illuminationoptical system of claim 29, wherein the depolarizer comprises a crystalprism including a crystal optic axis that is rotatable about an opticalaxis of the illumination optical system.
 31. The illumination opticalsystem of claim 29, wherein the depolarizer includes a polarized beamsplitter and a reflection system that returns light reflected by thepolarized beam splitter back to the polarized beam splitter byreflecting the light plural times in a plane such that a light path oflight that is transmitted through the polarized beam splitter and alight path of the light reflected by the polarized beam splittersubstantially match each other, the polarized beam splitter and thereflection system being integrally rotatable about an optical axis ofthe illumination optical system.
 32. The illumination optical system ofclaim 29, wherein the depolarizer includes a polarized beam splitter anda reflection system that returns light reflected by the polarized beamsplitter back to the polarized beam splitter by reflecting the lightplural times in a plane such that a light path of light that istransmitted through the polarized beam splitter and a light path of thelight reflected by the polarized beam splitter substantially match eachother, the polarized beam splitter and the reflection system beingintegrally insertable into and removable from the illumination lightpath.
 33. An illumination optical system that illuminates an illuminatedsurface with light from a light source that provides linearly polarizedlight, comprising: a polarized state switching device positioned in alight path between the light source and the illuminated surface, thepolarized state switching device switches a polarized state of the lightthat illuminates the illuminated surface between a predeterminedlinearly polarized state and a nonpolarized state while controlling aloss of light amount, wherein the polarized state switching devicecomprises a depolarizer that unpolarizes the incident linearly polarizedlight, and when switching the polarized state of the light thatilluminates the illuminated surface, light in a polarized state that hasnot been unpolarized by the depolarizer is directed to the depolarizer.34. The illumination optical system of claim 33, wherein the depolarizercomprises a crystal prism including a crystal optic axis extending in apredetermined direction.
 35. The illumination optical system of claim34, wherein when switching the polarized state of the light thatilluminates the illuminated surface, the linearly polarized light thatincludes a polarization plane in a direction of the crystal optic axisof the depolarizer is directed to the depolarizer.
 36. An illuminationoptical system that illuminates an illuminated surface with light from alight source that provides linearly polarized light, comprising: apolarized state switching device positioned in a light path between thelight source and the illuminated surface, the polarized state switchingdevice switches a polarized state of the light that illuminates theilluminated surface between a predetermined linearly polarized state anda nonpolarized state while controlling a loss of light amount: anillumination pupil distribution forming device that forms apredetermined light intensity distribution on or adjacent to a pupilplane of the illumination optical system; a changing device that changesat least one of a shape and a size of the predetermined light intensitydistribution; and a light direction optical system that directs a lightbeam including the predetermined light intensity distribution to theilluminated surface.
 37. The illumination optical system of claim 36,wherein the polarized state switching device changes a polarized stateof the light that illuminates the illuminated surface in accordance withthe change in at least one of the shape and the size of thepredetermined light intensity distribution.
 38. The illumination opticalsystem of claim 37, wherein the polarized state switching deviceswitches the polarized state of the light that illuminates theilluminated surface between the linearly polarized state and thenonpolarized state in accordance with the change in at least one of theshape and the size of the predetermined light intensity distribution.39. An illumination optical system that illuminates an illuminatedsurface with light from a light source that provides linearly polarizedlight, comprising: a polarized state switching device positioned in alight path between the light source and the illuminated surface, thepolarized state switching device switches a polarized state of the lightthat illuminates the illuminated surface between a predeterminedlinearly polarized state and a nonpolarized state while controlling aloss of light amount, wherein S1 and S2 components of a Stokes parameterof the light satisfy the below conditions in the nonpolarized state:|S1|≦0.1|S2|≦0.1.
 40. An exposure method, comprising: illuminating a maskthrough an illumination optical system; and exposing an image of apattern on the mask onto the photosensitive substrate positioned on theilluminated surface, wherein the illumination optical system illuminatesan illuminated surface with light from a light source that provideslinearly polarized light, the illumination optical system comprising: apolarized state switching device positioned in a light path between thelight source and the illuminated surface, the polarized state switchingdevice switches a polarized state of the light that illuminates theilluminated surface between a predetermined linearly polarized state anda nonpolarized state while controlling a loss of light amount.
 41. Theexposure method of claim 40, further comprising: forming the image ofthe pattern on the mask using a projection optical system; forming apredetermined light intensity distribution at a position conjugate to apupil of the projection optical system or a position adjacent thereto;and changing least one of a shape or a size of the predetermined lightintensity distribution.
 42. The exposure method of claim 41, wherein thechanging at least one of the shape or the size of the predeterminedlight intensity distribution changes at least one of the shape and thesize of the predetermined light intensity distribution in accordancewith pattern characteristics of the mask; the exposure method furthercomprises changing a polarized state of the light that illuminates theilluminated surface in accordance with a change in the at least one ofthe shape and the size of the predetermined light intensitydistribution.
 43. The exposure method of claim 42, wherein forming apredetermined light intensity distribution forms two areas including ahigh light intensity distribution spaced away from each other along apitch direction of a line-and-space pattern formed on the mask, theexposure method further comprising a step of setting the polarized stateof the light that illuminates the illuminated surface from the two areasincluding a high light intensity distribution to a linearly polarizedstate that includes a polarization plane in a direction substantiallyorthogonal to the pitch direction.
 44. The exposure method of claim 43,wherein the two areas including a high light intensity distribution areformed symmetrically about the optical axis of the illumination opticalsystem, and a value σo defined by a ratio φo/φp satisfies the followingcondition: 0.7≦σo where φo is a diameter of a circle about the opticalaxis that circumscribes the two areas including a high light intensitydistribution, and φp is a diameter of the pupil plane.
 45. The exposuremethod of claim 43, wherein the two areas including a high lightintensity distribution are formed symmetrically about the optical axisof the illumination optical system, and a value σo defined by a ratioφo/φp and σi defined by a ratio φi/φp satisfy the following condition:0.5≦σi/σo where φo is a diameter of a circle about the optical axis thatcircumscribes the two areas including a high light intensitydistribution, φp is a diameter of the pupil plane, and φi is a diameterof a circle about the optical axis that inscribes the two areasincluding a high light intensity distribution.
 46. An illuminationoptical system that illuminates an illuminated surface with light from alight source that provides linearly polarized light, comprising: apolarized state switching device positioned in a light path between thelight source and the illuminated surface, the polarized state switchingdevice switches a polarized state of the light that illuminates theilluminated surface between a predetermined linearly polarized state anda nonpolarized state while controlling a loss of light amount: apolarization monitor positioned in a downstream light path of thepolarized state switching device to detect the polarized state of thelight, and a controller that controls the polarized state switchingdevice in response to an output from the polarization monitor.
 47. Anexposure method for exposing a pattern on a mask positioned at a firstplane onto a photosensitive substrate positioned at a second plane,comprising: providing linearly polarized light; illuminating the maskwith the provided light; exposing the pattern on the illuminated maskonto the photosensitive substrate; and switching a polarized state ofthe light on the second plane between a predetermined linearly polarizedstate and a nonpolarized state while controlling a loss of a lightamount.
 48. The exposure method of claim 47, wherein the switching thepolarized state includes varying a polarization plane for the linearlypolarized light.
 49. The exposure method of claim 47, wherein theexposing the pattern includes forming an image of the pattern on themask onto the second plane using a projection optical system, theexposure method further comprising: forming a predetermined lightintensity distribution at a position conjugate to a pupil of theprojection optical system or a position adjacent thereto; changing atleast one of a shape and a size of the predetermined light intensitydistribution; and changing a polarized state of the light thatilluminates the illuminated surface in accordance with the change in atleast one of the shape and the size of the predetermined light intensitydistribution.
 50. An illumination optical system that illuminates anilluminated surface with light from a light source that provideslinearly polarized light, comprsing: a polarized state switching devicepositioned in a light path between the light source and the illuminatedsurface, the polarized state switching device switches a polarized stateof the light that illuminates the illuminated surface between apredetermined polarized state and a nonpolarized state while controllinga loss of light amount; a polarization monitor positioned in adownstream light path of the polarized state switching device to detectthe polarized state of the light; and a controller that controls thepolarized state switching device in response to an output from thepolarization monitor.
 51. The illumination optical system of claim 50,wherein the polarized state switching device comprises a half-wave plateincluding a crystal optic axis that is rotatable about the optical axisof the illumination optical system, and a quarter-wave plate including acrystal optic axis that is rotatable about the optical axis of theillumination optical system, and in response to changes in detectionresults obtained from the polarization monitor when respectivelychanging the crystal optic axes of the quarter-wave plate and thehalf-wave plate, the controller adjusts an angular position of thecrystal optic axis of the quarter-wave plate to a predetermined positionfor converting incident elliptically polarized light into linearlypolarized light and an angular position of the crystal optic axis of thehalf-wave plate to a predetermined position for converting incidentlinearly polarized light into linearly polarized light that includes apolarization plane in a predetermined direction.
 52. The illuminationoptical system of claim 51, wherein the controller adjusts the angularposition of the crystal optic axis of the quarter-wave plate to a firstangular position, at which a contrast for changes in an S1 component ofthe Stokes parameter in the detection result becomes substantiallymaximum when the crystal optic axis of the quarter-wave plate ischanged, and the angular position of the crystal optic axis of thehalf-wave plate to a second angular position, at which the S1 componentof the Stokes parameter in the detection result becomes substantiallymaximum or substantially minimum when the crystal optic axis of thehalf-wave plate is changed while the crystal optic axis of thequarter-wave plate is set at the first angular position.
 53. Theillumination optical system of claim 52, wherein the polarizationmonitor is positioned in the light path between the polarized stateswitching device and the illuminated surface and includes a beamsplitter that extracts from the light path reflected light ortransmitted light in a polarized state different from the polarizedstate of the incident light, and a light intensity detector that detectsan intensity of the reflected light or the transmitted light extractedby the beam splitter, and the polarized state of the incident light tothe beam splitter is detected based on an output of the light intensitydetector.
 54. An exposure apparatus, comprising the illumination opticalsystem of claim
 50. 55. The exposure apparatus of claim 54, furthercomprising: a projection optical system positioned in the light pathbetween a first plane at which a mask is positioned, and a second planeat which a photosensitive substrate is positioned, the projectionoptical system forming an image of a pattern on the mask onto the secondplane; a pupil intensity distribution forming device that forms apredetermined light intensity distribution at a position conjugate to apupil of the projection optical system or a position adjacent thereto;and a pupil intensity distribution changing device that changes at leastone of a shape and a size of the predetermined light intensitydistribution.
 56. The exposure apparatus of claim 55, further comprisinga polarized state changing device that is positioned in the light pathbetween the light source and the illuminated surface and changes thepolarized state of the light that illuminates the illuminated surface,wherein the pupil intensity distribution changing device changes atleast one of the shape and the size of the predetermined light intensitydistribution in accordance with pattern characteristics of the mask, andthe polarized state changing device changes the polarized state of thelight that illuminates the illuminated surface in accordance with atleast one of the shape and the size of the predetermined light intensitydistribution.
 57. The exposure apparatus of claim 56, wherein thepolarized state changing device comprises the polarized state switchingdevice that switches the polarized state of the light that illuminatesthe illuminated surface between a predetermined polarized state and anonpolarized state, and the polarized state switching device switchesbetween the predetermined polarized state and the nonpolarized state inaccordance with a change in at least one of the shape and the size ofthe predetermined light intensity distribution.
 58. An exposure method,comprising: illuminating a mask through the illumination optical systemof claim 50; and exposing an image of a pattern on the mask onto thephotosensitive substrate positioned on the illuminated surface.